a(n) = P_{2n}(sqrt(2))/sqrt(2) (see A155100).

A156122

a(n) = P_{2n}(sqrt(2))/sqrt(2) (see A155100).

Terms

    a(0) =1a(1) =6a(2) =192a(3) =15216a(4) =2249472a(5) =534437376a(6) =186227300352

External references