Partial sums of A001372.

Terms

a(0) =1a(1) =2a(2) =5a(3) =12a(4) =31a(5) =78a(6) =208a(7) =551a(8) =1502a(9) =4117a(10) =11435a(11) =31926a(12) =89829a(13) =253727a(14) =719926a(15) =2048919a(16) =5848543a(17) =16732592a(18) =47973762a(19) =137788720a(20) =396393362a(21) =1141962118a(22) =3294080424a(23) =9512949813a(24) =27501182865a(25) =79579492065a(26) =230478715333