a(n) = (6^(n+1) - (-5)^(n+1))/11.

Terms

a(0) =1a(1) =1a(2) =31a(3) =61a(4) =991a(5) =2821a(6) =32551a(7) =117181a(8) =1093711a(9) =4609141a(10) =37420471a(11) =175694701a(12) =1298308831a(13) =6569149861a(14) =45518414791a(15) =242592910621