A058501 Primes p such that largest odd factor of p-1 is not a prime (i.e., is composite or 1).

2, 3, 5, 17, 19, 31, 37, 43, 61, 67, 71, 73, 79, 101, 103, 109, 127, 131, 139, 151, 157, 163, 181, 191, 197, 199, 211, 223, 229, 239, 241, 251, 257, 271, 277, 281, 283, 307, 311, 313, 331, 337, 349, 367, 373, 379, 397, 401, 409, 419, 421, 431, 433, 439, 443

Offset: 1

Author

Labos Elemer, Dec 20 2000

Keywords

• nonn

Examples

			127 is here because 127 - 1 = 126 = 2*63 and 63 is not a prime. 2 is here because 2 - 1 = 1 = 1*2^0 and 1 is not a prime.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A057023, A006093.

Programs

Mathematica

lofQ[n_]:=Module[{c=Select[Divisors[n-1],OddQ][[-1]]},!PrimeQ[c]]; Select[ Prime[ Range[100]],lofQ] (* Harvey P. Dale, Jul 24 2021 *)

Formula

Nonprimes in A057023.