a(n) = 5*binomial(7*n+5,n)/(7*n+5).

Terms

a(0) =1a(1) =5a(2) =45a(3) =500a(4) =6200a(5) =82251a(6) =1142295a(7) =16398200a(8) =241379325a(9) =3623534200a(10) =55262073757a(11) =853814730600