Apply partial sum operator twice to factorials.

Terms

a(0) =0a(1) =1a(2) =3a(3) =7a(4) =17a(5) =51a(6) =205a(7) =1079a(8) =6993a(9) =53227a(10) =462341a(11) =4500255a(12) =48454969a(13) =571411283a(14) =7321388397a(15) =101249656711