A247221 Numbers k such that 2*k^2 + 1 divides 2^k + 1.
0, 1, 67653, 2124804
Offset: 1
Programs
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Magma
[n: n in [1..300000] | Denominator((2^n+1)/(2*n^2+1)) eq 1];
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Mathematica
a247221[n_Integer] := Select[Range[n], Divisible[2^# + 1, 2*#^2 + 1] &]; a247221[2500000] (* Michael De Vlieger, Nov 30 2014 *)
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PARI
for(n=0,10^9,if(Mod(2,2*n^2+1)^n==-1,print1(n,", "))); \\ Joerg Arndt, Nov 30 2014
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Python
A247221_list = [n for n in range(10**6) if pow(2,n,2*n*n+1) == 2*n*n] # Chai Wah Wu, Dec 07 2014
Comments