seen = 0
unseen = 1

K = 5

other(p) = my (v=unseen); while (bittest(seen, v) || #factor(p*v)~<K, v++); return (v)

for (n=1, 25 000, a = other(n); seen += 2^a; while (bittest(seen, unseen), unseen++); print (n " " a))

quit