Partial sums of A097893.

Terms

a(0) =1a(1) =3a(2) =8a(3) =20a(4) =51a(5) =133a(6) =356a(7) =972a(8) =2695a(9) =7557a(10) =21372a(11) =60840a(12) =174097a(13) =500295a(14) =1442720a(15) =4172752a(16) =12099411a(17) =35161001a(18) =102375400a(19) =298586652a(20) =872177273a(21) =2551118623a(22) =7471195500a(23) =21904500500a(24) =64286141881a(25) =188844619563a(26) =555216323396