A319370 Composite numbers k such that phi(k)^phi(k) == k + 1 (mod k^2).
91, 18227, 28605, 137481, 538849, 2832797, 3220333, 384792005
Offset: 1
Programs
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PARI
isok(n) = n>1 && !isprime(n) && Mod(n-eulerphi(n), n^2)^eulerphi(n)==1;
This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
isok(n) = n>1 && !isprime(n) && Mod(n-eulerphi(n), n^2)^eulerphi(n)==1;
Select[Range[20000], Divisible[EulerPhi[#]^EulerPhi[#] - 1, #^2] &] (* Vaclav Kotesovec, Oct 21 2018 *) Join[{1},Select[Range[1851*10^5],With[{c=EulerPhi[#]},PowerMod[c,c,#^2] == 1&]]] (* Harvey P. Dale, Oct 09 2020 *)
isok(n) = Mod(eulerphi(n), n^2)^eulerphi(n)==1; for(n=1, 10000000, if(isok(n),print1(n, ", ")))
isok(n) = Mod(2, n^2)^(n*(n+1)/2)==-1;
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