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%I #3 Mar 31 2012 20:02:01
%S 1,575,202605639573839041,478502736827135487987972323577847681
%N Positive integers n such that for every k in [n,n+1,n+2,n+3,n+4] we have sigma(k) coprime to k.
%C Note that it is impossible to have three consecutive positive even integers which have odd sigma() values.
%C In order to have an odd sigma() value, the integer must be a square or twice a square; it's not too hard to see that three consecutive positive even integers can't each be a square or twice a square.
%C So any solution must have n odd and among n+1 and n+3, one of them must be a square and the other must be twice a square.
%C Any other terms exceed 10^128.
%K nonn
%O 1,2
%A _Jack Brennen_, Mar 17 2008
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