M(M-1)/2, where M is Mersenne prime A000668(n).

A139224

M(M-1)/2, where M is Mersenne prime A000668(n).

Terms

    a(0) =3a(1) =21a(2) =465a(3) =8001a(4) =33542145a(5) =8589737985a(6) =137438167041

External references