a(n) = product{ p primes <= n+1 such that p divides n+1 or p-1 divides n }.

Terms

a(0) =1a(1) =2a(2) =6a(3) =2a(4) =30a(5) =6a(6) =42a(7) =2a(8) =30a(9) =10a(10) =66a(11) =6a(12) =2730a(13) =14a(14) =30a(15) =2a(16) =510a(17) =6a(18) =798a(19) =10a(20) =2310a(21) =22a(22) =138a(23) =6a(24) =2730a(25) =26a(26) =6a(27) =14a(28) =870a(29) =30