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Primes whose first and last number is 3: Difference between revisions
Primes whose first and last number is 3 (view source)
Revision as of 12:29, 24 July 2021
, 2 years ago→{{header|REXX}}: added the computer programming language REXX.
m (added whitespace and the requirement of base ten numbers.) |
(→{{header|REXX}}: added the computer programming language REXX.) |
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9349 9419 9439 9479 9539 9619 9629 9649 9679 9689
9719 9739 9749 9769 9829 9839 9859 9929 9949</pre>
=={{header|REXX}}==
<lang ring>/*REXX pgm finds and displays primes (base ten) that contain a leading and trailing 3. */
parse arg hi cols dig . /*obtain optional argument from the CL.*/
if hi=='' | hi=="," then hi= 4000 /*Not specified? Then use the default.*/
if cols=='' | cols=="," then cols= 10 /* " " " " " " */
if dig=='' | dig=="," then dig= 3 /* " " " " " " */
call genP /*build array of semaphores for primes.*/
w= 10 /*width of a number in any column. */
title= ' primes N (in base ten) that have a leading and ending digit of ' dig ,
" where N < " commas(hi)
if cols>0 then say ' index │'center(title, 1 + cols*(w+1) )
if cols>0 then say '───────┼'center("" , 1 + cols*(w+1), '─')
found= 0; idx= 1 /*initialize # of primes found; IDX. */
$= /*list of primes that contain a string.*/
do j=1 for # /*find primes with leading/trailing dig*/
parse var @.j Ld 2 '' -1 Td /*obtain the leading and trailing digit*/
if Ld\==dig then iterate /*does prime contain a leading DIG ? */ /* ◄■■■■■■■ a filter.*/
if Td\==dig then iterate /* " " " " trailing ? ? */ /* ◄■■■■■■■ a filter.*/
found= found + 1 /*bump the number of primes found. */
if cols<0 then iterate /*Build the list (to be shown later)? */
c= commas(@.j) /*maybe add commas to the number. */
$= $ right(c, max(w, length(c) ) ) /*add a prime ──► $ list, allow big #*/
if found//cols\==0 then iterate /*have we populated a line of output? */
say center(idx, 7)'│' substr($, 2); $= /*display what we have so far (cols). */
idx= idx + cols /*bump the index count for the output*/
end /*j*/
if $\=='' then say center(idx, 7)"│" substr($, 2) /*possible display residual output.*/
if cols>0 then say '───────┴'center("" , 1 + cols*(w+1), '─')
say
say 'Found ' commas(found) title
exit 0 /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
commas: parse arg ?; do jc=length(?)-3 to 1 by -3; ?=insert(',', ?, jc); end; return ?
/*──────────────────────────────────────────────────────────────────────────────────────*/
genP: @.1=2; @.2=3; @.3=5; @.4=7; @.5=11 /*define some low primes. */
!.=0; !.2=1; !.3=1; !.5=1; !.7=1; !.11=1 /* " " " " semaphores. */
#=5; sq.#= @.# **2 /*number of primes so far; prime². */
do j=@.#+2 by 2 to hi-1 /*find odd primes from here on. */
parse var j '' -1 _; if _==5 then iterate /*J divisible by 5? (right dig)*/
if j// 3==0 then iterate /*" " " 3? */
if j// 7==0 then iterate /*" " " 7? */
do k=5 while sq.k<=j /* [↓] divide by the known odd primes.*/
if j // @.k == 0 then iterate j /*Is J ÷ X? Then not prime. ___ */
end /*k*/ /* [↑] only process numbers ≤ √ J */
#= #+1; @.#= j; sq.#= j*j; !.j= 1 /*bump # of Ps; assign next P; P²; P# */
end /*j*/; return</lang>
{{out|output|text= when using the default inputs:}}
<pre>
index │ primes N (in base ten) that have a leading and ending digit of 3 where N < 4,000
───────┼───────────────────────────────────────────────────────────────────────────────────────────────────────────────
1 │ 3 313 353 373 383 3,023 3,083 3,163 3,203 3,253
11 │ 3,313 3,323 3,343 3,373 3,413 3,433 3,463 3,533 3,583 3,593
21 │ 3,613 3,623 3,643 3,673 3,733 3,793 3,803 3,823 3,833 3,853
31 │ 3,863 3,923 3,943
───────┴───────────────────────────────────────────────────────────────────────────────────────────────────────────────
Found 33 primes N (in base ten) that have a leading and ending digit of 3 where N < 4,000
</pre>
=={{header|Ring}}==
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