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%I #19 Feb 08 2016 10:14:26
%S 24,54,121,304,780,2352,127744,430272,33501184,184773312,8589082624
%N Sporadic solutions to sigma(n) == 12 modulo n.
%C Terms of A076496 that are either not divisible by 6 or such that x/6 is not coprime to 6.
%C 10384593717069654320312270165377024 is also a term. - _Donovan Johnson_, Dec 23 2013
%H A. Anavi, P. Pollack, C. Pomerance, <a href="http://dx.doi.org/10.1142/S1793042112501266">On congruences of the form sigma(n) == a (mod n)</a>, Int. J. Number Theory 09, 115 (2013).
%H P. Pollack, <a href="http://alpha.math.uga.edu/~pollack/CNTA2012.pdf">The sum of divisors of n, modulo n</a>, CNTA 2012.
%e sigma(24) % 24 = 12, and 24/6 is not coprime to 6, hence 24 is here.
%e sigma(121) % 121 = 12, and 121 is not divisible by 6, hence 121 is here.
%o (PARI) a(n) = m = 6; a = sigma(m) ; ((sigma(n) % n) == a) && ((n % m) || (!(n % m) && (gcd(m, (n/m)) != 1)));
%Y Cf. A076496.
%Y Supersequence of A084306.
%K nonn,more
%O 1,1
%A _Michel Marcus_, Dec 21 2013
%E a(11) from _Donovan Johnson_, Dec 23 2013
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