%I #5 Mar 30 2012 18:39:22
%S 1,4,12,16,25,28,32,35,36,48,49,52,55,64,65,76,77,80,84,85,91,92,95,
%T 96,108,112,115,119,121,124,125,133,143,144,145,148,155,156,160,161,
%U 164,169,172,175,185,187,188,192,196,203,205,208,209,212,215,217,221,228
%N Nonprimes n such that 3*(3^n1)*B(2n) is an integer, where B(k) denotes the kth Bernoulli number.
%C It appears that a(n) is never == 2 (mod 4)
%o (PARI) a(n)=denominator(bernfrac(2*prime(n)))
%K nonn
%O 1,2
%A _Benoit Cloitre_, Feb 11 2004
