T(2n,n-2), T given by A027907.

Terms

a(0) =1a(1) =6a(2) =36a(3) =210a(4) =1221a(5) =7098a(6) =41328a(7) =241128a(8) =1409895a(9) =8260934a(10) =48497064a(11) =285219090a(12) =1680166215a(13) =9912297150a(14) =58558256496a(15) =346371955776