OFFSET
1,2
COMMENTS
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
MAPLE
with(numtheory):
rad:= n-> mul(i, i=factorset(n)):
a:= proc(n) option remember; local k; for k from 1+a(n-1)
while phi(rad(k))<>rad(phi(k)) do od; k
end: a(0):=0:
seq(a(n), n=1..80); # Alois P. Heinz, Jun 07 2013
MATHEMATICA
rad[n_] := Product[fa[n][[i, 1]], {i,
Length[fa[n]]}]; fa = FactorInteger;
Select[Range[500], rad[EulerPhi[#]] == EulerPhi[rad[#]] &]
PROG
(PARI) is(n)=my(f=factor(n)); lcm(factor(eulerphi(f))[, 1])==prod(i=1, #f~, f[i, 1]-1) \\ Charles R Greathouse IV, Nov 13 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
José María Grau Ribas, Jun 05 2013
STATUS
approved