a(n) = (1/18)*(9*n^2 + 21*n + 10 - 4^(n+2)*(3*n+5) + 10*7^(n+1)).
A142976
a(n) = (1/18)*(9*n^2 + 21*n + 10 - 4^(n+2)*(3*n+5) + 10*7^(n+1)).
Terms
- a(0) =1a(1) =39a(2) =546a(3) =5482a(4) =47175a(5) =373809a(6) =2824048a(7) =20729340a(8) =149474205a(9) =1065892555a(10) =7547929806a(11) =53215791774a(12) =374165893891
External references
- oeis: A142976