A071965 Numbers k such that k = Gpf(k) * Gpf(sigma(k)) where Gpf(k) = A006530(k) is the greatest prime factor of k.

15, 33, 51, 69, 91, 95, 141, 145, 159, 213, 287, 295, 321, 395, 445, 473, 573, 581, 679, 703, 745, 895, 973, 995, 1139, 1149, 1169, 1195, 1199, 1293, 1339, 1345, 1441, 1561, 1717, 1757, 1795, 1891, 1941, 2051, 2147, 2167, 2245, 2353, 2395, 2443, 2495, 2589

Offset: 1

Author

Benoit Cloitre, Jun 16 2002

Keywords

• easy
• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000203, A006530, A071190.

Programs

Mathematica

Select[Range[2,3000],FactorInteger[#][[-1,1]]FactorInteger[ DivisorSigma[ 1,#]] [[-1,1]]==#&] (* Harvey P. Dale, Sep 15 2011 *)

PARI

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