a(n) = (39^n - 1)/38.A218742a(n) = (39^n - 1)/38.Terms a(0) =0a(1) =1a(2) =40a(3) =1561a(4) =60880a(5) =2374321a(6) =92598520a(7) =3611342281a(8) =140842348960External referencesoeis: A218742