a(n) is the denominator of Sum_{i=1..n} i!/(i^2).

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =3a(5) =15a(6) =15a(7) =105a(8) =105a(9) =105a(10) =105a(11) =1155a(12) =1155a(13) =15015a(14) =15015a(15) =15015a(16) =15015a(17) =255255a(18) =255255a(19) =4849845a(20) =4849845a(21) =4849845a(22) =4849845a(23) =111546435a(24) =111546435a(25) =111546435a(26) =111546435a(27) =111546435a(28) =111546435a(29) =3234846615