a(0)=1, a(1)=1, a(n) = 3*a(n-1) + a(n-2) + 1.

Terms

a(0) =1a(1) =1a(2) =5a(3) =17a(4) =57a(5) =189a(6) =625a(7) =2065a(8) =6821a(9) =22529a(10) =74409a(11) =245757a(12) =811681a(13) =2680801a(14) =8854085a(15) =29243057a(16) =96583257a(17) =318992829a(18) =1053561745a(19) =3479678065a(20) =11492595941a(21) =37957465889a(22) =125364993609a(23) =414052446717