a(1) = 2; for n > 1, a(n) = 3*a(n-1) + 3 - n.

Terms

a(0) =2a(1) =7a(2) =21a(3) =62a(4) =184a(5) =549a(6) =1643a(7) =4924a(8) =14766a(9) =44291a(10) =132865a(11) =398586a(12) =1195748a(13) =3587233a(14) =10761687a(15) =32285048a(16) =96855130a(17) =290565375a(18) =871696109a(19) =2615088310a(20) =7845264912a(21) =23535794717a(22) =70607384131a(23) =211822152372a(24) =635466457094