G.f. A(x) satisfies A(x) = 1/(1 - x/(1 - x*A(x)))^4.

Terms

a(0) =1a(1) =4a(2) =14a(3) =60a(4) =297a(5) =1584a(6) =8868a(7) =51412a(8) =305964a(9) =1858308a(10) =11472152a(11) =71774548a(12) =454080514a(13) =2899959640a(14) =18670920458a(15) =121056521536a(16) =789733186076