

A066228


The EulerPhi(sigma(EulerPhi))perfect numbers, where the fperfect numbers for an arithmetical function f are defined in A066218.


0




OFFSET

1,1


COMMENTS

There are no terms between 449 and 10^5. Are there any more terms? Are there infinitely many?


LINKS



EXAMPLE

Let f(n) = EulerPhi(sigma(EulerPhi(n)). Proper divisors of 28 = {1, 2, 4, 7, 14}; the sum of their fvalues = 1+1+2+4+4 = 12 = f(28); hence 28 belongs to the sequence.


MATHEMATICA

f[x_] := EulerPhi[DivisorSigma[1, EulerPhi[x]]]; Select[ Range[ 1, 10^5], 2 * f[ # ] == Apply[ Plus, Map[ f, Divisors[ # ] ] ] & ]


CROSSREFS



KEYWORD

nonn,more


AUTHOR



EXTENSIONS



STATUS

approved



