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A206449 Values of sigma(p) of primes p such that sigma(p) = sigma(c) has solution for some composite number c. 0

%I #12 Feb 10 2014 01:35:04

%S 12,18,24,32,42,48,54,60,72,80,84,90,98,104,108,114,128,132,140,152,

%T 168,180,182,192,224,228,234,240,252,264,270,272,294,308,312,360,384,

%U 390,420,432,434,440,444,450,468,480,492,504,522,558,570,572,588,594,600

%N Values of sigma(p) of primes p such that sigma(p) = sigma(c) has solution for some composite number c.

%C Corresponding values of sigma(p) of primes p from A158913.

%F a(n) = A158913(n) + 1.

%t Union@ Select[ DivisorSigma[1, Select[ Range@ 100, !PrimeQ@# &]], PrimeQ[# - 1] &] (* _Robert G. Wilson v_, Feb 09 2012 *)

%Y Cf. A158913 (primes p such that there is a composite c with sigma(p)=sigma(c)), A206448 (values of sigma(c) of composite numbers c such that sigma(c) = sigma(d) has solution for any other composite number d), A000203.

%K nonn

%O 1,1

%A _Jaroslav Krizek_, Feb 07 2012

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Last modified March 28 18:04 EDT 2024. Contains 371254 sequences. (Running on oeis4.)