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%I #9 Apr 28 2017 22:34:51
%S 55,65,77,91,115,125,161,175,185,187,209,221,235,245,247,259,295,305,
%T 319,329,341,343,355,365,377,391,403,413,415,425,427,437,451,473,475,
%U 485,497,511,533,535,545,559,581,583,595,605,629,655,665
%N Composite numbers of the form 12*k+5 or 12*k+7 for some k.
%C Conjecture: Let r(n) = (a(n)-1)/(a(n)+1)) if a(n) mod 4 = 1, (a(n)+1)/(a(n)-1)) otherwise; then Product_{n>=1} r(n) = (28/27) * (32/33) * (38/39) * (46/45) * ... = 1.
%p remove(isprime, [seq(seq(12*k+j,j=[5,7]),k=1..100)]); # _Robert Israel_, Apr 28 2017
%o (PARI) {
%o for(n=0,100,
%o n12=12*n;n5=n12+5;n7=n12+7;
%o if(!isprime(n5),print1(n5", "));
%o if(!isprime(n7),print1(n7", "))
%o )
%o }
%K nonn
%O 1,1
%A _Dimitris Valianatos_, Apr 26 2017
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