a(n) = binomial(2^n + 2, n).A136506a(n) = binomial(2^n + 2, n).Terms a(0) =1a(1) =4a(2) =15a(3) =120a(4) =3060a(5) =278256a(6) =90858768a(7) =105637584000External referencesoeis: A136506