cp's OEIS Frontend

A228567 Primes expressible as sigma(sigma(n)) - sigma(n), in order of their occurrence.

%I A228567 #20 Dec 31 2013 05:33:48
%S A228567 3,7,17,31,31,41,23,73,127,73,89,127,463,523,241,523,157,241,523,463,
%T A228567 211,257,131,983,379,1153,311,1153,83,983,521,4339,4339,113,8893,4339,
%U A228567 4339,1093,4339,769,2851,8893,4339,1429,1097,4339,1093,4339,8893,4339,8893
%N A228567 Primes expressible as sigma(sigma(n)) - sigma(n), in order of their occurrence.
%H A228567 K. D. Bajpai, <a href="/A228567/b228567.txt">Table of n, a(n) for n = 1..2200</a>
%e A228567 a(9)= 127: sigma(sigma(93))-sigma(93)= 255-128= 127, which is prime.
%e A228567 a(11)= 89: sigma(sigma(98))-sigma(98)= 260-171= 89, which is prime.
%p A228567 with(numtheory):KD := proc() local a; a:= sigma(sigma(n))-sigma(n);if isprime(a) then RETURN (a); fi; end: seq(KD(),n=1..5000);
%Y A228567 Cf. A000203 (sigma(n): sum of divisors of n).
%Y A228567 Cf. A019279 (superperfect numbers: sigma(sigma(n))=2n).
%Y A228567 Cf. A033632 (numbers n: sigma(n)is prime).
%Y A228567 Cf. A051027 (sigma(sigma(n))).
%K A228567 nonn
%O A228567 1,1
%A A228567 _K. D. Bajpai_, Nov 10 2013