OFFSET
1,2
COMMENTS
Numbers k such that rad(psi(k)) = rad(k), where rad(k) is the squarefree kernel of k (A007947).
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
6 is in the sequence since 6 = 2 * 3 and psi(6) = 12 = 2^2 * 3 have the same set of prime divisors, {2, 3}.
MATHEMATICA
rad[n_] := Times @@ (First@# & /@ FactorInteger@ n); psi[1] = 1; psi[n_] := n * Times @@ (1 + 1/Transpose[FactorInteger[n]][[1]]); Select[Range[2000], rad[psi[#]] == rad[#] &]
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Nov 23 2019
STATUS
approved