a(n) is the smallest m such that n!-m and n!+m are both primes.

Terms

a(0) =0a(1) =1a(2) =5a(3) =7a(4) =19a(5) =19a(6) =31a(7) =17a(8) =11a(9) =17a(10) =83a(11) =67a(12) =353a(13) =227a(14) =163a(15) =59a(16) =61a(17) =113a(18) =353a(19) =31a(20) =1447a(21) =571a(22) =389a(23) =191a(24) =337a(25) =883a(26) =101a(27) =1823a(28) =659a(29) =709