Special neighbor primes: Difference between revisions

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@.1=2; @.2=3; @.3=5; @.4=7; @.5=11 /*define some low primes. */

!.2=1; !.3=1; !.5=1; !.7=1; !.11=1 /* " " " " flags. */

#=5; s.#= @.# **2 /*number of primes so far; prime². */

#=5; sq.#= @.# **2 /*number of primes so far; prime². */

/* [↓] generate more primes ≤ high.*/

do j=@.#+2 by 2 to limit /*find odd primes from here on. */

parse var j '' -1 _; if _==5 then iterate /*J ~~divisible~~ by 5? (right ~~dig~~)*/

parse var j '' -1 _; if _==5 then iterate /*J ÷ by 5? (right digit).*/

if j// 3==0 then iterate /*" " " 3? */

if j//3==0 then iterate; if j//7==0 then iterate /*" " " 3? J ÷ by 7? */

if ~~j// 7==0 then iterate~~ /*~~" " " 7?~~ */

do k=5 while sq.k<=j /* [↓] divide by the known odd primes.*/

/* [↑] the above 3 lines saves time.*/

do k=5 while s.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; s.#= j*j; !.j= 1 /*bump # of Ps; assign next P; P²; P# */

#= #+1; @.#= j; sq.#= j*j; !.j= 1 /*bump # of Ps; assign next P; P²; P# */

end /*j*/; return</lang>

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