a(n) = A026907(2*n, n-1).

Terms

a(0) =28a(1) =154a(2) =627a(3) =2414a(4) =9201a(5) =35094a(6) =134259a(7) =515302a(8) =1983678a(9) =7656374a(10) =29619728a(11) =114822606a(12) =445925707a(13) =1734610302a(14) =6757306947a(15) =26358212502a(16) =102937963242a(17) =402444721782