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A374823 Primes p such that p-1 is refactorable.

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%I A374823 #13 Dec 12 2024 22:55:59
%S A374823 2,3,13,19,37,41,61,73,89,97,109,137,157,181,229,233,241,277,349,373,
%T A374823 397,449,569,601,613,641,673,709,733,809,829,853,857,877,881,883,937,
%U A374823 997,1049,1069,1097,1117,1153,1193,1201,1213,1237,1249,1361,1409,1433,1549,1621,1657,1669,1693,1789,1801
%N A374823 Primes p such that p-1 is refactorable.
%C A374823 Primes p such that p - 1 is divisible by A000005(p-1), the number of divisors of p - 1.
%H A374823 Robert Israel, <a href="/A374823/b374823.txt">Table of n, a(n) for n = 1..10000</a>
%e A374823 a(4) = 19 is a term because 19 is prime and 18 is divisible by A000005(18) = 6.
%p A374823 filter:= p -> isprime(p) and (p-1) mod numtheory:-tau(p-1) = 0:
%p A374823 select(filter, [2, seq(i,i=3..10000,2)]);
%Y A374823 Intersection of A000040 and A377121.
%Y A374823 Includes A158018 and A158014 (except 17).
%Y A374823 Cf. A000005, A033950.
%K A374823 nonn
%O A374823 1,1
%A A374823 _Robert Israel_, Dec 12 2024