Partial sums of A012814.

Terms

a(0) =0a(1) =1a(2) =6a(3) =27a(4) =113a(5) =464a(6) =1896a(7) =7738a(8) =31571a(9) =128800a(10) =525455a(11) =2143647a(12) =8745216a(13) =35676948a(14) =145547524a(15) =593775045a(16) =2422362078a(17) =9882257735a(18) =40315615409a(19) =164471408184a(20) =670976837020