a(n) = 6 * binomial(2*n,n-1) + binomial(2*n-1,n).

Terms

a(0) =7a(1) =27a(2) =100a(3) =371a(4) =1386a(5) =5214a(6) =19734a(7) =75075a(8) =286858a(9) =1100138a(10) =4232592a(11) =16328942a(12) =63146500a(13) =244711260a(14) =950094810a(15) =3694876515a(16) =14390571690a(17) =56122547250a(18) =219140635560a(19) =856617714810