a(n) = T(2n+2,n), array T as in A055818.

Terms

a(0) =1a(1) =11a(2) =60a(3) =328a(4) =1800a(5) =9924a(6) =54964a(7) =305680a(8) =1706256a(9) =9554620a(10) =53653996a(11) =302038488a(12) =1703995800a(13) =9631951476a(14) =54539233380a(15) =309296779296