a(n+1) = Sum_{k=1..n} (a(k) + k*(n-k)), with a(1)=1.

Terms

a(0) =1a(1) =2a(2) =7a(3) =20a(4) =50a(5) =115a(6) =251a(7) =530a(8) =1096a(9) =2237a(10) =4529a(11) =9124a(12) =18326a(13) =36743a(14) =73591a(15) =147302a(16) =294740a(17) =589633a(18) =1179437a(19) =2359064a(20) =4718338a(21) =9436907a(22) =18874067a(23) =37748410a(24) =75497120a(25) =150994565a(26) =301989481a(27) =603979340a(28) =1207959086