Largest prime dividing Sum_{k=0..n} k! * (n-k)!.

Terms

a(0) =2a(1) =5a(2) =2a(3) =2a(4) =13a(5) =151a(6) =3a(7) =83a(8) =73a(9) =1433a(10) =647a(11) =29a(12) =28211a(13) =337a(14) =19a(15) =73a(16) =18181a(17) =130349a(18) =771079a(19) =731957a(20) =6619a(21) =4111a(22) =61927a(23) =140001721a(24) =42829a(25) =774885169a(26) =745984697a(27) =41711914513a(28) =34311919a(29) =117695654963