T(2n,n+4), T given by A026780.

Terms

a(0) =1a(1) =11a(2) =80a(3) =489a(4) =2732a(5) =14512a(6) =74888a(7) =380329a(8) =1916709a(9) =9637687a(10) =48528434a(11) =245289395a(12) =1246499970a(13) =6374296278a(14) =32816505566a(15) =170106486358a(16) =887697088316