A027996 a(n)=Sum{T(n,k)*T(n,k+2)}, 0<=k<=2n-2, T given by A027926.
6, 26, 106, 424, 1684, 6667, 26352, 104069, 410806, 1621325, 6398688, 25254823, 99691822, 393600358, 1554333406, 6139498384, 24256359424, 95857063972, 378903471934, 1498090689910, 5924490920776, 23435015022946, 92721024432286
Offset: 2