1,1

All terms are prime of the form 4n+3 belonging to A002145(n). A002145(n) is a union of a(n) and A129517(n) = Odd primes p such that p divides (p-1)!!-1.

Select[Range[3, 2000], IntegerQ[((#-2)!!-1)/# ]&&IntegerQ[((#-3)!!-1)/# ]&]

Cf. A006882 = Double factorials n!!. Cf. A002145 = Primes of form 4n+3. Cf. A129517 = Odd primes p such that p divides (p-1)!!-1. Cf. A129516 = numbers n such that n divides (n-1)!!-1.

Sequence in context: A003758 A000231 A132565 this_sequence A007670 A074714 A064457

Adjacent sequences: A129515 A129516 A129517 this_sequence A129519 A129520 A129521

nonn

Alexander Adamchuk (alex(AT)kolmogorov.com), Apr 18 2007