a(n) = 2^n + 3^n - n.

Terms

a(0) =2a(1) =4a(2) =11a(3) =32a(4) =93a(5) =270a(6) =787a(7) =2308a(8) =6809a(9) =20186a(10) =60063a(11) =179184a(12) =535525a(13) =1602502a(14) =4799339a(15) =14381660a(16) =43112241a(17) =129271218a(18) =387682615a(19) =1162785736a(20) =3487832957a(21) =10462450334a(22) =31385253891a(23) =94151567412a(24) =282446313673a(25) =847322163850