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A058501 Primes p such that largest odd factor of p-1 is not a prime (i.e., is composite or 1). 2

%I

%S 2,3,5,17,19,31,37,43,61,67,71,73,79,101,103,109,127,131,139,151,157,

%T 163,181,191,197,199,211,223,229,239,241,251,257,271,277,281,283,307,

%U 311,313,331,337,349,367,373,379,397,401,409,419,421,431,433,439,443

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

%H Amiram Eldar, <a href="/A058501/b058501.txt">Table of n, a(n) for n = 1..10000</a>

%F Nonprimes in A057023.

%e 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.

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

%Y Cf. A057023, A006093.

%K nonn

%O 1,1

%A _Labos Elemer_, Dec 20 2000

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Last modified February 7 12:58 EST 2023. Contains 360123 sequences. (Running on oeis4.)