a(n) = A047848(n, n).

Terms

a(0) =1a(1) =2a(2) =7a(3) =44a(4) =401a(5) =4682a(6) =66431a(7) =1111112a(8) =21435889a(9) =469070942a(10) =11488207655a(11) =311505013052