Column 3 of array in A265080.

Terms

a(0) =0a(1) =3a(2) =12a(3) =51a(4) =192a(5) =675a(6) =2358a(7) =8043a(8) =26736a(9) =88659a(10) =290910a(11) =941985a(12) =3046068a(13) =9791613a(14) =31221414a(15) =99466515a(16) =315677664a(17) =996398883a(18) =3143147598a(19) =9888728505a(20) =30988353300a(21) =97066250379a(22) =303448558578a(23) =945804661377