OFFSET
1,2
LINKS
Harry J. Smith, Table of n, a(n) for n=1,...,1000
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