%I #9 Feb 02 2016 12:06:11
%S 1,1,2,5,15,10,14,16,3,0,13,18,10,16,19,17,20,3,7,5,7,15,9,16,3,19,19,
%T 1,17,11,12,1,17,13,18,0,16,6,4,16,10,11,2,15,10,20,19,0,6,10,18,16,4,
%U 19,20,2,0,13,20,16,18,15,16,6,19,1,13,5,17,15,4,20,7,18,15,4,12,10,13,4,5
%N Bell numbers (A000110) read mod 21.
%H G. C. Greubel, <a href="/A146111/b146111.txt">Table of n, a(n) for n = 0..10000</a>
%H W. F. Lunnon, P. A. B. Pleasants, and N. M. Stephens, <a href="http://matwbn.icm.edu.pl/ksiazki/aa/aa35/aa3511.pdf">Arithmetic properties of Bell numbers to a composite modulus I</a>, Acta Arithmetica 35 (1979), pp. 1-16.
%F a(n+1784341) = a(n). - _G. C. Greubel_, Feb 02 2016
%t Mod[BellB[Range[0,80]],21] (* _Harvey P. Dale_, Sep 04 2012 *)
%Y Cf. A000110, A146108, A146109, A146110, A146112, A146113, A146114.
%K nonn
%O 0,3
%A _N. J. A. Sloane_, Feb 07 2009