M(M-1)/6, where M is Mersenne prime A000668(n).

A139226

M(M-1)/6, where M is Mersenne prime A000668(n).

Terms

    a(0) =1a(1) =7a(2) =155a(3) =2667a(4) =11180715a(5) =2863245995a(6) =45812722347

External references