a(n) = A000041(2^n - 1).A173301a(n) = A000041(2^n - 1).Terms a(0) =1a(1) =1a(2) =3a(3) =15a(4) =176a(5) =6842a(6) =1505499a(7) =3913864295External referencesoeis: A173301