Partial sums of A005036.

Terms

a(0) =1a(1) =2a(2) =4a(3) =9a(4) =25a(5) =85a(6) =346a(7) =1589a(8) =7846a(9) =40567a(10) =216327a(11) =1180227a(12) =6554627a(13) =36939883a(14) =210777514a(15) =1215644593a(16) =7077255068a(17) =41546269583a(18) =245708229893