a(n) is the product of primes p such that p+1 divides n.

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =1a(5) =10a(6) =1a(7) =21a(8) =2a(9) =1a(10) =1a(11) =330a(12) =1a(13) =13a(14) =2a(15) =21a(16) =1a(17) =170a(18) =1a(19) =57a(20) =2a(21) =1a(22) =1a(23) =53130a(24) =1a(25) =1a(26) =2a(27) =39a(28) =1a(29) =290