Partial sums of A215602.

Terms

a(0) =2a(1) =5a(2) =17a(3) =45a(4) =122a(5) =320a(6) =842a(7) =2205a(8) =5777a(9) =15125a(10) =39602a(11) =103680a(12) =271442a(13) =710645a(14) =1860497a(15) =4870845a(16) =12752042a(17) =33385280a(18) =87403802a(19) =228826125a(20) =599074577a(21) =1568397605a(22) =4106118242a(23) =10749957120a(24) =28143753122a(25) =73681302245a(26) =192900153617a(27) =505019158605