Sum of the divisors of 3^n-1.

Terms

a(0) =3a(1) =15a(2) =42a(3) =186a(4) =399a(5) =1680a(6) =3282a(7) =15876a(8) =31836a(9) =123690a(10) =277344a(11) =1541568a(12) =2391486a(13) =8992680a(14) =25483332a(15) =111757968a(16) =193819392a(17) =967814400a(18) =1744488660a(19) =9366647892a(20) =16912999320a(21) =62424587520a(22) =144219337920a(23) =852903426816