Erdős-primes: Difference between revisions
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→{{header|REXX}}: added the computer programming language REXX. |
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=={{header|REXX}}== |
=={{header|REXX}}== |
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<lang rexx>/*REXX program counts and shows the number of Erdős primes under a specified number N. */ |
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<lang rexx></lang> |
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parse arg n cols . /*get optional number of primes to find*/ |
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if n=='' | n=="," then n= 500 /*Not specified? Then assume default.*/ |
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if cols=='' | cols=="," then cols= 10 /* " " " " " .*/ |
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Ocols= cols; cols= abs(cols) /*Use the absolute value of cols. */ |
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call genP n /*generate all primes under N. */ |
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primes= 0 /*initialize the number of Erdős primes*/ |
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$= /*a list of Erdős primes (so far). */ |
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do j=1 until j>=n /*lets now search for Erdős primes. */ |
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if \!.j then iterate /*Is J not a prime? Then skip it. */ |
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_= sumDigs(j); if \!._ then iterate /*Is sum of J's digs a prime? No, skip.*/ |
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primes= primes + 1 /*bump the count of Erdős primes. */ |
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if Ocols<1 then iterate /*Build the list (to be shown later)? */ |
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$= $ right(j, w) /*add the Erdős prime to the $ list. */ |
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if primes//cols\==0 then iterate /*have we populated a line of output? */ |
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say substr($, 2); $= /*display what we have so far (cols). */ |
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end /*j*/ |
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if $\=='' then say substr($, 2) /*possible display some residual output*/ |
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say |
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say 'found ' primes " Erdős primes < " n |
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exit 0 /*stick a fork in it, we're all done. */ |
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/*──────────────────────────────────────────────────────────────────────────────────────*/ |
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sumDigs: parse arg x 1 s 2; do k=2 for length(x)-1; s= s + substr(x,k,1); end; return s |
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/*──────────────────────────────────────────────────────────────────────────────────────*/ |
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genP: parse arg n; @.=.; @.1=2; @.2=3; @.3=5; @.4=7; @.5=11; @.6=13; @.7=17; #= 7 |
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w= length(n); !.=0; !.2=1; !.3=1; !.5=1; !.7=1; !.11=1; !.13=1; !.17=1 |
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do j=@.7+2 by 2 while j<n /*continue on with the next odd prime. */ |
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parse var j '' -1 _ /*obtain the last digit of the J var.*/ |
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if _ ==5 then iterate /*is this integer a multiple of five? */ |
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if j // 3 ==0 then iterate /* " " " " " " three? */ |
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/* [↓] divide by the primes. ___ */ |
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do k=4 to # while k*k<=j /*divide J by other primes ≤ √ J */ |
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if j//@.k == 0 then iterate j /*÷ by prev. prime? ¬prime ___ */ |
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end /*k*/ /* [↑] only divide up to √ J */ |
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#= # + 1; @.#= j; !.j= 1 /*bump prime count; assign prime & flag*/ |
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end /*j*/ |
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return</lang> |
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{{out|output|text= when using the default inputs:}} |
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<pre> |
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2 3 5 7 11 23 29 41 43 47 |
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61 67 83 89 101 113 131 137 139 151 |
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157 173 179 191 193 197 199 223 227 229 |
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241 263 269 281 283 311 313 317 331 337 |
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353 359 373 379 397 401 409 421 443 449 |
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461 463 467 487 |
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found 54 Erdős primes < 500 |
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</pre> |
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=={{header|Ring}}== |
=={{header|Ring}}== |
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