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%I #25 Sep 02 2017 13:44:30
%S 751,919,1502,1838,2841,3788,5682,6629,8523,11251,11937,13258,13669,
%T 14205,15137,15152,15397,15607,15916,16099,17046,18940,19895,22502,
%U 22728,23874,27338,28410,30103,30274,30304,30794,31214,31832,32198,36853,37880,39790,43657
%N Numbers m such that psi(x) = phi(m) has a solution while sigma(y) = phi(m) has none.
%C Values of A069825(k) such that psi(x) = phi(A069825(k)) has a solution for k > 1.
%C Prime terms are 751, 919, 11251, 13669, 15137, ...
%e 751 is a term because psi(x) = phi(751) = 750 has a solution that is x = 625 while there is no solution for sigma(y) = phi(751) = 750.
%o (PARI) is1(n) = my(N=eulerphi(n)); for(k=1, N, if(sigma(k)==N, return(1))); 0;
%o a001615(n) = my(f=factor(n)); prod(i=1, #f~, f[i, 1]^f[i, 2] + f[i, 1]^(f[i, 2]-1));
%o is2(n) = my(N=eulerphi(n)); for(k=1, N, if(a001615(k)==N, return(1))); 0;
%o isok(n) = !is1(n) && is2(n); \\ after _Charles R Greathouse IV_ at A001615
%Y Cf. A000010, A000203, A001615, A069825.
%K nonn
%O 1,1
%A _Altug Alkan_, Aug 25 2017
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