Special neighbor primes: Difference between revisions
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(Add Factor) |
(→{{header|REXX}}: changed program to use neighbor primes.) |
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=={{header|REXX}}== |
=={{header|REXX}}== |
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The output list is displayed in numerical order by prime '''P''' and then by prime '''Q'''. |
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parse arg hi cols . /*obtain optional argument from the CL.*/ |
parse arg hi cols . /*obtain optional argument from the CL.*/ |
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if hi=='' | hi=="," then hi= 100 /*Not specified? Then use the default.*/ |
if hi=='' | hi=="," then hi= 100 /*Not specified? Then use the default.*/ |
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if cols=='' | cols=="," then cols= 5 /* " " " " " " */ |
if cols=='' | cols=="," then cols= 5 /* " " " " " " */ |
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call genP hi /*build semaphore array for low primes.*/ |
call genP hi /*build semaphore array for low primes.*/ |
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do p=1 while @.p<hi |
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end /*p*/; lim= p-1; q= p+1 /*set LIM to prime for P; calc. 2nd HI.*/ |
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#m= # - 1 |
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w= 20 /*width of a number in any column. */ |
w= 20 /*width of a number in any column. */ |
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title= ' special neighbor primes: |
title= ' special neighbor primes: P1, P2, P1+P2-1 are primes, and P1 and P2 < ' , |
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if cols>0 then say ' |
if cols>0 then say ' index │'center(title, 1 + cols*(w+1) ) |
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found= 0; idx= 1 /*init. # special neighbor primes & IDX*/ |
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found= 0; idx= 1 /*initialize # neighbor primes & index.*/ |
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$= /*a list of neighbor primes (so far).*/ |
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do j=1 to lim; jp= j+1; q= @.jp /*look for neighbor primes within range*/ |
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y= @.j + q - 1; if \!.y then iterate /*is X also a prime? No, then skip it.*/ |
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found= found + 1 /*bump the number of neighbor primes. */ |
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if cols==0 then iterate /*Build the list (to be shown later)? */ |
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$= $ right( @.j','q"──►"y, w) /*add neighbor prime ──► the $ list. */ |
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if found//cols\==0 then iterate /*have we populated a line of output? */ |
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say center(idx, 7)'│' substr($, 2); $= /*display what we have so far (cols). */ |
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idx= idx + cols /*bump the index count for the output*/ |
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idx= idx + cols /*bump the index count for the output*/ |
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end /*j*/ |
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if $\=='' then say center(idx, 7)"│" substr($, 2) /*possible display residual output.*/ |
if $\=='' then say center(idx, 7)"│" substr($, 2) /*possible display residual output.*/ |
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if cols>0 then say '───────┴'center("" , 1 + cols*(w+1), '─') |
if cols>0 then say '───────┴'center("" , 1 + cols*(w+1), '─') |
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say |
say |
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say 'Found ' commas(found) title |
say 'Found ' commas(found) title |
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@.1=2; @.2=3; @.3=5; @.4=7; @.5=11 /*define some low primes. */ |
@.1=2; @.2=3; @.3=5; @.4=7; @.5=11 /*define some low primes. */ |
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!.2=1; !.3=1; !.5=1; !.7=1; !.11=1 /* " " " " flags. */ |
!.2=1; !.3=1; !.5=1; !.7=1; !.11=1 /* " " " " flags. */ |
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#=5; |
#=5; s.#= @.# **2 /*number of primes so far; prime². */ |
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/* [↓] generate more primes ≤ high.*/ |
/* [↓] generate more primes ≤ high.*/ |
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do j=@.#+2 by 2 to limit /*find odd primes from here on. */ |
do j=@.#+2 by 2 to limit /*find odd primes from here on. */ |
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parse var |
parse var j '' -1 _; if _==5 then iterate /*J divisible by 5? (right dig)*/ |
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if j// 3==0 then iterate /*" " " 3? */ |
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if j// 7==0 then iterate /*" " " 7? */ |
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/* [↑] the above 3 lines saves time.*/ |
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do k=5 while s.k<=j /* [↓] divide by the known odd primes.*/ |
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if j // @.k == 0 then iterate j /*Is J ÷ X? Then not prime. ___ */ |
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end /*k*/ /* [↑] only process numbers ≤ √ J */ |
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#= #+1; @.#= j; s.#= j*j; !.j= 1 /*bump # of Ps; assign next P; P²; P# */ |
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end /*j*/; return</lang> |
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{{out|output|text= when using the default inputs:}} |
{{out|output|text= when using the default inputs:}} |
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<pre> |
<pre> |
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index │ |
index │ special neighbor primes: P1, P2, P1+P2-1 are primes, and P1 and P2 < 100 |
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───────┼────────────────────────────────────────────────────────────────────────────────────────────────────────── |
───────┼────────────────────────────────────────────────────────────────────────────────────────────────────────── |
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1 │ 3,5──►7 |
1 │ 3,5──►7 5,7──►11 7,11──►17 11,13──►23 13,17──►29 |
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6 │ |
6 │ 19,23──►41 29,31──►59 31,37──►67 41,43──►83 43,47──►89 |
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11 │ |
11 │ 61,67──►127 67,71──►137 73,79──►151 |
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21 │ 7,37──►43 7,41──►47 7,47──►53 7,53──►59 7,61──►67 |
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26 │ 7,67──►73 7,73──►79 7,83──►89 7,97──►103 11,13──►23 |
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31 │ 11,19──►29 11,31──►41 11,37──►47 11,43──►53 11,61──►71 |
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36 │ 11,73──►83 11,79──►89 11,97──►107 13,17──►29 13,19──►31 |
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41 │ 13,29──►41 13,31──►43 13,41──►53 13,47──►59 13,59──►71 |
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46 │ 13,61──►73 13,67──►79 13,71──►83 13,89──►101 13,97──►109 |
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51 │ 17,31──►47 17,37──►53 17,43──►59 17,67──►83 17,73──►89 |
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56 │ 17,97──►113 19,23──►41 19,29──►47 19,41──►59 19,43──►61 |
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61 │ 19,53──►71 19,61──►79 19,71──►89 19,79──►97 19,83──►101 |
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66 │ 19,89──►107 23,31──►53 23,37──►59 23,61──►83 23,67──►89 |
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71 │ 23,79──►101 29,31──►59 29,43──►71 29,61──►89 29,73──►101 |
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76 │ 29,79──►107 31,37──►67 31,41──►71 31,43──►73 31,53──►83 |
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81 │ 31,59──►89 31,67──►97 31,71──►101 31,73──►103 31,79──►109 |
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86 │ 31,83──►113 31,97──►127 37,43──►79 37,47──►83 37,53──►89 |
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91 │ 37,61──►97 37,67──►103 37,71──►107 37,73──►109 41,43──►83 |
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96 │ 41,61──►101 41,67──►107 41,73──►113 41,97──►137 43,47──►89 |
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101 │ 43,59──►101 43,61──►103 43,67──►109 43,71──►113 43,89──►131 |
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106 │ 43,97──►139 47,61──►107 47,67──►113 53,61──►113 53,79──►131 |
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111 │ 53,97──►149 59,73──►131 59,79──►137 61,67──►127 61,71──►131 |
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116 │ 61,79──►139 61,89──►149 61,97──►157 67,71──►137 67,73──►139 |
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121 │ 67,83──►149 67,97──►163 71,79──►149 71,97──►167 73,79──►151 |
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126 │ 79,89──►167 83,97──►179 |
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───────┴────────────────────────────────────────────────────────────────────────────────────────────────────────── |
───────┴────────────────────────────────────────────────────────────────────────────────────────────────────────── |
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Found |
Found 13 special neighbor primes: P1, P2, P1+P2-1 are primes, and P1 and P2 < 100 |
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</pre> |
</pre> |
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