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A065875
Numbers k such that usigma(phi(k)) is a prime.
1
3, 4, 5, 6, 8, 10, 12, 17, 32, 34, 40, 48, 60, 257, 512, 514, 544, 640, 680, 768, 816, 960, 1020, 65537, 131072, 131074, 131584, 139264, 139808, 163840, 164480, 174080, 174760, 196608, 197376, 208896, 209712, 245760, 246720, 261120, 262140
OFFSET
1,1
COMMENTS
The only odd terms below 10^7 are 3, 5, 17, 257 & 65537.
PROG
(PARI) u(n)=sumdivmult(n, d, if(gcd(d, n/d)==1, d));
for(n=1, 10^5, if(isprime(u(eulerphi(n))), print1(n, ", "))); \\ Joerg Arndt, Sep 17 2023
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Dec 07 2001
EXTENSIONS
Deleted incorrect MMA program. - N. J. A. Sloane, Sep 17 2023
STATUS
approved