T(2n,n+2), T given by A026780.

Terms

a(0) =1a(1) =7a(2) =38a(3) =191a(4) =935a(5) =4547a(6) =22166a(7) =108790a(8) =538668a(9) =2692996a(10) =13594954a(11) =69281309a(12) =356222591a(13) =1846781939a(14) =9647229202a(15) =50744420578a(16) =268591503348