5726797824domain: NAppears in sequencesa(n) = sigma((4^n - 1)/3), where sigma(n) is the sum of positive divisors of n.at n=16A102359a(1)=1, a(2)=1, a(3)=4, a(4)=0; a(n)=12a(n-2)-16a(n-3) for n>=5.at n=18A123016Sum of the divisors of A001045(n) (Jacobsthal numbers).at n=33A366772