A226384 - OEIS

%I #17 Apr 09 2020 09:58:35

%S 1,2,3,6,7,11,12,14,22,23,24,28,31,43,44,46,47,48,56,59,62,67,71,79,

%T 83,86,88,92,94,96,103,107,112,118,124,131,134,139,142,158,166,167,

%U 172,176,179,184,188,191,192,206,211,214,223,224,227,236,239,248,262

%N Numbers k such that rad(phi(k)) = phi(rad(k)).

%C Numbers k such that A080400(k) = A173557(k). - _Amiram Eldar_, Apr 09 2020

%H Charles R Greathouse IV, <a href="/A226384/b226384.txt">Table of n, a(n) for n = 1..10000</a>

%p with(numtheory):

%p rad:= n-> mul(i, i=factorset(n)):

%p a:= proc(n) option remember; local k; for k from 1+a(n-1)

%p       while phi(rad(k))<>rad(phi(k)) do od; k

%p     end: a(0):=0:

%p seq(a(n), n=1..80);  # _Alois P. Heinz_, Jun 07 2013

%t rad[n_] := Product[fa[n][[i, 1]], {i,

%t      Length[fa[n]]}]; fa = FactorInteger;

%t       Select[Range[500], rad[EulerPhi[#]] == EulerPhi[rad[#]] &]

%o (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

%Y Cf. A000010, A007947, A080400, A173557.

%K nonn

%O 1,2

%A _José María Grau Ribas_, Jun 05 2013