a(n) = Sum_{k=0..2n} (k+1) * A026323(n, 2n-k).

Terms

a(0) =1a(1) =6a(2) =27a(3) =81a(4) =243a(5) =729a(6) =2187a(7) =6561a(8) =19683a(9) =59049a(10) =177147a(11) =531441a(12) =1594323a(13) =4782969a(14) =14348907a(15) =43046721a(16) =129140163a(17) =387420489a(18) =1162261467a(19) =3486784401a(20) =10460353203a(21) =31381059609a(22) =94143178827a(23) =282429536481a(24) =847288609443