A convolution of binomial coefficients.

Terms

a(0) =1a(1) =1a(2) =1a(3) =8a(4) =77a(5) =824a(6) =9448a(7) =113728a(8) =1419349a(9) =18215576a(10) =239034104a(11) =3194168768a(12) =43331889928a(13) =595375647424