a(n) = (3^(n+2)+11)/2 - 5*2^(n+1) + 2*n.

Terms

a(0) =0a(1) =1a(2) =10a(3) =53a(4) =218a(5) =789a(6) =2658a(7) =8581a(8) =26986a(9) =83477a(10) =255506a(11) =776709a(12) =2350554a(13) =7092565a(14) =21359554a(15) =64242437a(16) =193054922a(17) =579820053a(18) =1740770802a(19) =5224933765a(20) =15680044090a(21) =47050617941a(22) =141172825250a(23) =423560418693