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.
Table of n, a(n) for n=2..44.
Cf. A014574, A068525, A075590, A181490.
Sequence in context: A223346 A109510 A034715 * A079390 A124679 A242949
Adjacent sequences: A294727 A294728 A294729 * A294731 A294732 A294733
Hugo Pfoertner, Nov 08 2017