a(n) = 7*binomial(4*n + 7, n)/(4*n + 7).

Terms

a(0) =1a(1) =7a(2) =49a(3) =357a(4) =2695a(5) =20930a(6) =166257a(7) =1344904a(8) =11042724a(9) =91801255a(10) =771201431a(11) =6536904290a(12) =55838330730a(13) =480197194260