a(n) = f(n,n) where f is given in A034261.

Terms

a(0) =0a(1) =1a(2) =7a(3) =39a(4) =196a(5) =930a(6) =4257a(7) =19019a(8) =83512a(9) =361998a(10) =1553630a(11) =6615686a(12) =27992472a(13) =117823940a(14) =493768485a(15) =2061580275a(16) =8580127920a(17) =35611376790a(18) =147447066690a(19) =609200868210