a(n) = n! * Sum_{k=1..n} floor(n/k)/k.

Terms

a(0) =1a(1) =5a(2) =23a(3) =134a(4) =814a(5) =6324a(6) =50028a(7) =475824a(8) =4806576a(9) =54597600a(10) =644119200a(11) =8847100800a(12) =121718332800