Exponential-convolution of triangular numbers with themselves.

Terms

a(0) =1a(1) =6a(2) =30a(3) =128a(4) =486a(5) =1692a(6) =5512a(7) =17040a(8) =50496a(9) =144512a(10) =401664a(11) =1089024a(12) =2890240a(13) =7529472a(14) =19298304a(15) =48754688a(16) =121602048a(17) =299827200a(18) =731643904a(19) =1768685568a(20) =4239261696a(21) =10081796096a(22) =23805296640a(23) =55839817728a(24) =130187001856a(25) =301813727232a(26) =696036360192