OFFSET
1,2
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..74 (terms below 5*10^10)
EXAMPLE
3 is in the sequence since usigma(uphi(3)) = usigma(2) = 3.
MATHEMATICA
usigma[1] = 1; usigma[n_] := Times @@ (1 + Power @@@ FactorInteger[n]); uphi[1] = 1; uphi[n_] := Times @@ (-1 + Power @@@ FactorInteger[n]); Select[Range[10^4], usigma[uphi[#]] == # &]
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Nov 22 2019
STATUS
approved