Main diagonal of the triangular array A161136.

Terms

a(0) =1a(1) =3a(2) =9a(3) =18a(4) =80a(5) =196a(6) =554a(7) =1824a(8) =2292a(9) =7218a(10) =45522a(11) =288135a(12) =660113a(13) =3201130a(14) =10512530a(15) =17675063a(16) =191230544a(17) =207521990