The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.
Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations
(which often say "discovered thanks to the OEIS").
It is conjectured that a(n)=0 for prime n with the only exceptions given by n=A181490(k)+1, i.e. a(2)=6, a(3)=12, a(7)=192 and a(19)=786432 are the only currently known exceptions.