Diagonal sums of a Chebyshev number triangle.

Terms

a(0) =1a(1) =0a(2) =0a(3) =1a(4) =3a(5) =3a(6) =8a(7) =30a(8) =117a(9) =466a(10) =1960a(11) =8655a(12) =40391a(13) =200085a(14) =1051888a(15) =5844844a(16) =34131049a(17) =208344660a(18) =1324262256a(19) =8743620525a(20) =59891078347a(21) =425216195191