A026074 a(n) = T(3n,n), where T is the array defined in A024996.
1, 1, 12, 91, 726, 5902, 48704, 406353, 3419020, 28958955, 246598716, 2109182557, 18106771400, 155929895685, 1346442959176, 11653675471305, 101071521560286, 878176794266261, 7642505705447340, 66606583068846975
Offset: 0