s = 0 unseen = 1 seen(v) = bit test(s, v) see(v) = s = bit or(s, 2^v); while (seen(unseen), unseen++) other(pp) = { for (v=unseen, oo, if (!seen(v) && gcd(pp, v)==1, return (v); ); ); } { a = vector(10 000); \\ A225047 u = 1; for (n=1, oo, see(v=if (n<=2, unseen, other(pp))); if (v<=#a, a[v] = n; while (a[u], print (u " " u-a[u]); if (u++>#a, break (2); ); ); ); [pp,p] = [p,v]; ); } quit