Ulam spiral (for primes): Difference between revisions
→{{header|ZX Spectrum Basic}}
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=={{header|ZX Spectrum Basic}}==
a simplistic naive procedure that on a real machine will take some DAYS at the max of 176x176 numbers to check
RUN 10 , to start
<syntaxhighlight lang="ZX Spectrum Basic">
1 IF n<max THEN LET n=n+1: FOR p=2 TO n-1: LET r= (INT (n/p)<>n/p): IF r THEN NEXT p
2 IF p=n THEN LET pr=pr+1: LET kx=(255-xx AND k<3)+(xx AND k>2): LET ky=(175-yy AND (k=1 OR k=3)+(yy AND (k=2 OR k=4))): PLOT kx,ky: PRINT #0;AT 0,0;n;" pr";pr
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