NB. Stanislaw Uram's prime spiral pattern by T. Nishikawa 2001/10/22 NB. 「素数の不思議」, 好田順治著,現代数学社, p.56-58 NB. spiral n -> returns pattern of 1 to (2*n+1)^2 NB. adjust to J8 by m.shimura 05/2018 NB. Usage:(prime 1 spiralp 3) {'.*' -> Uram’s Small Pattern NB. Usage:(prime 41 spiralp 19) {'.*' -> Uram’s Large Pattern spiral =: 3 : 0 S=. 1 1$1 N=: }: 2+i. *: 1+2*y (north @ west @ south @ east) ^:(y) S ) east =: 3 : 0 N=: t}. N [ m0=. t{.N [ t=. {. $y y ,. m0 ) south =: 3 : 0 N=: t}.N [ m0=. t{.N [ t=. {: $y y , |. m0 ) west =: 3 : 0 N=: t}.N [ m0=. t{.N [ t=. {. $y (|.m0) ,. y ) north =: 3 : 0 N=: t}.N [ m0=. t{.N [ t=. {: $y m0, y ) spiralp =: 4 : 0 u0=: <: x + *: 1 + 2 * y r=. >: u0 - x t=. -: <: %: r S=. 1 1$x N =: (>: x) to u0 (north @ west @ south @ east) ^:(t) S ) to =: 4 : 0 x + i. >: y - x ) prime =: 1: = #@q: