A071965 - OEIS

%I #16 Jun 02 2022 14:48:33

%S 15,33,51,69,91,95,141,145,159,213,287,295,321,395,445,473,573,581,

%T 679,703,745,895,973,995,1139,1149,1169,1195,1199,1293,1339,1345,1441,

%U 1561,1717,1757,1795,1891,1941,2051,2147,2167,2245,2353,2395,2443,2495,2589

%N Numbers k such that k = Gpf(k) * Gpf(sigma(k)) where Gpf(k) = A006530(k) is the greatest prime factor of k.

%H Amiram Eldar, <a href="/A071965/b071965.txt">Table of n, a(n) for n = 1..10000</a>

%t Select[Range[2,3000],FactorInteger[#][[-1,1]]FactorInteger[ DivisorSigma[ 1,#]] [[-1,1]]==#&] (* _Harvey P. Dale_, Sep 15 2011 *)

%o (PARI) for(n=1,3000,if(vecmax(component(factor(n),1))*vecmax(component(factor(sigma(n)),1))==n,print1(n,",")))

%Y Cf. A000203, A006530, A071190.

%K easy,nonn

%O 1,1

%A _Benoit Cloitre_, Jun 16 2002