a(n) = A131770( n*(n+1)/2 ) for n>=0.

Terms

a(0) =1a(1) =2a(2) =8a(3) =32a(4) =156a(5) =820a(6) =4744a(7) =29544a(8) =196708a(9) =1388012a(10) =10320096a(11) =80474620a(12) =655800496a(13) =5569011668a(14) =49164525468a(15) =450312766892