OFFSET
1,1
COMMENTS
These are all the terms less than 10^5. Problem: Find an expression generating all the terms.
LINKS
J. Pe, On a Generalization of Perfect Numbers, J. Rec. Math., 31(3) (2002-2003), 168-172.
EXAMPLE
Let f(n) = sigma(EulerPhi(n)). The proper divisors of 88 are {1, 2, 4, 8, 11, 22, 44}; adding their f-values: 1 + 1 + 3 + 7 + 18 + 18 + 42 = 90 = f(88). Hence 88 is a term of the sequence.
MATHEMATICA
f[x_] := DivisorSigma[1, EulerPhi[x]]; Select[ Range[ 1, 10^5], 2 * f[ # ] == Apply[ Plus, Map[ f, Divisors[ # ] ] ] & ]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Joseph L. Pe, Dec 18 2001
EXTENSIONS
a(6)-a(13) from Amiram Eldar, Sep 26 2019
STATUS
approved