Left factorials: !n = Sum_{k=0..n-1} k!.

Terms

a(0) =0a(1) =1a(2) =2a(3) =4a(4) =10a(5) =34a(6) =154a(7) =874a(8) =5914a(9) =46234a(10) =409114a(11) =4037914a(12) =43954714a(13) =522956314a(14) =6749977114a(15) =93928268314