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A065556
Numbers n such that sigma (phi ( n ) ) = sigma (sigma (n ) ) where phi is Euler's totient and sigma is the multiplicative sum-of-divisors function.
1
1, 367, 919, 1967, 3641, 4379, 5143, 7379, 11843, 12767, 13493, 15293, 21797, 26039, 28381, 29807, 30263, 30593, 30599, 30887, 37523, 40199, 48559, 49781, 51101, 51397, 55277, 62573, 67223, 72433, 73979, 87047, 89255, 89851, 95393
OFFSET
1,2
LINKS
FORMULA
sigma(phi(n)) = sigma(sigma(n)).
EXAMPLE
367 is in the sequence because phi(367) = 366, sigma(367) = 368, sigma(366) = 744 = sigma(368).
MATHEMATICA
Select[Range[100000], DivisorSigma[1, EulerPhi[#]]==DivisorSigma[ 1, DivisorSigma[1, #]]&] (* Harvey P. Dale, Jun 23 2013 *)
PROG
(PARI) { n=0; for (m=1, 10^9, if (sigma(eulerphi(m)) == sigma(sigma(m)), write("b065556.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Oct 22 2009
CROSSREFS
KEYWORD
nonn
AUTHOR
Walter Nissen, Nov 28 2001
STATUS
approved