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Odd numbers k such that A007733(k) is even but 2^x == -1 (mod k) is insoluble.
2

%I #8 Aug 26 2021 09:47:28

%S 15,21,35,39,45,51,55,63,69,75,77,85,87,91,93,95,105,111,115,117,119,

%T 123,133,135,141,143,147,153,155,159,165,175,183,187,189,195,203,207,

%U 213,215,219,221,225,231,235,237,245,247,253,255,259,261,267,273,275,279,285,287

%N Odd numbers k such that A007733(k) is even but 2^x == -1 (mod k) is insoluble.

%Y Set difference of A296243 and A014657.

%Y Cf. A002326, A007733.

%K nonn

%O 1,1

%A _Max Alekseyev_, Dec 09 2017