A247205 Numbers k such that 2*k^2 - 1 divides 2^k - 1.
1, 18480, 8388480
Offset: 1
Examples
1 is in this sequence because 2*1^2 - 1 = 1 divides 2^1 - 1 = 1.
Programs
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Magma
[n: n in [1..100000] | Denominator((2^n-1)/(2*n^2-1)) eq 1];
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PARI
for(n=1,10^9,if(Mod(2,2*n^2-1)^n==+1,print1(n,", "))); \\ Joerg Arndt, Nov 30 2014
Extensions
a(3) from Joerg Arndt, Nov 30 2014
Comments