a(n) = binomial(3*n,n)*(5*n+2)/(2*n+1).

Terms

a(0) =2a(1) =7a(2) =36a(3) =204a(4) =1210a(5) =7371a(6) =45696a(7) =286824a(8) =1817046a(9) =11593725a(10) =74397180a(11) =479634480a(12) =3104160696a(13) =20155648324a(14) =131239189440a(15) =856606186128