a(n) = Sum_{k=1..n} 2^T(k-1), where T = A000217 are the triangular numbers 0, 1, 3, 6, 10, ... . For n=0 we have the empty sum equal to 0.

A181388

a(n) = Sum_{k=1..n} 2^T(k-1), where T = A000217 are the triangular numbers 0, 1, 3, 6, 10, ... . For n=0 we have the empty sum equal to 0.

Terms

    a(0) =0a(1) =1a(2) =3a(3) =11a(4) =75a(5) =1099a(6) =33867a(7) =2131019a(8) =270566475a(9) =68990043211

External references