Sum of the divisors of 5^n-1.

Terms

a(0) =7a(1) =60a(2) =224a(3) =1736a(4) =6048a(5) =49920a(6) =136724a(7) =1107792a(8) =3718400a(9) =27060480a(10) =85449224a(11) =869499904a(12) =2136230474a(13) =15820920000a(14) =61359427584a(15) =461863805760