A048120 a(n)=T(2n,n+1), where T is given by A048113.
0, 0, 2, 6, 24, 84, 312, 1140, 4248, 15852, 59688, 225624, 857424, 3270216, 12518472, 48062520, 185034360, 714038448, 2761343064, 10698992304, 41525207448, 161418403008, 628356425856, 2449152822168, 9557303840184
Offset: 1