Sum_{T(i,j)}, 0<=j<=i, 0<=i<=n, where T is the array in A026386.

Terms

a(0) =3a(1) =7a(2) =17a(3) =37a(4) =87a(5) =187a(6) =437a(7) =937a(8) =2187a(9) =4687a(10) =10937a(11) =23437a(12) =54687a(13) =117187a(14) =273437a(15) =585937a(16) =1367187a(17) =2929687a(18) =6835937a(19) =14648437a(20) =34179687a(21) =73242187a(22) =170898437a(23) =366210937a(24) =854492187a(25) =1831054687a(26) =4272460937a(27) =9155273437a(28) =21362304687a(29) =45776367187