a(n) = f(n,n+2) where f is given in A034261.

Terms

a(0) =0a(1) =1a(2) =11a(3) =76a(4) =435a(5) =2255a(6) =11011a(7) =51688a(8) =236028a(9) =1056210a(10) =4654430a(11) =20266312a(12) =87402185a(13) =374008635a(14) =1590144675a(15) =6724160400a(16) =28303504680a(17) =118665923310a(18) =495820606410