a(n) = least k such that the remainder when 21^k is divided by k is n.
2, 19, 6, 17, 218, 15, 14, 13, 12, 11, 86, 9249, 214, 133, 69, 4084085, 106, 39, 422
1 seqfan posts
Tue Aug 11 01:35:14 CEST 2009 [seqfan] Re: Dead b-files for A127816 and others