This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A071964 #14 Oct 28 2024 09:35:58 %S A071964 4,6,9,10,21,25,34,39,49,55,57,111,121,155,169,203,205,219,253,289, %T A071964 291,301,305,327,361,489,497,505,514,529,579,689,737,755,791,841,889, %U A071964 905,961,979,1027,1081,1205,1255,1299,1355,1369,1379,1461,1477,1681,1703 %N A071964 Numbers k such that k = Gpf(k) * Gpf(phi(k)) where Gpf(k) = A006530(k) is the greatest prime factor of k. %H A071964 Amiram Eldar, <a href="/A071964/b071964.txt">Table of n, a(n) for n = 1..10000</a> %t A071964 Select[Range[1800],FactorInteger[#][[-1,1]]FactorInteger[EulerPhi[#]][[-1,1]] == #&] (* _Harvey P. Dale_, Mar 25 2023 *) %o A071964 (PARI) for(n=1,3000,if(vecmax(component(factor(n),1))*vecmax(component(factor(eulerphi(n)),1))==n,print1(n,","))) %o A071964 (PARI) is(k) = if(k > 2, my(f = factor(k)); k == f[#f~, 1] * vecmax(factor(eulerphi(f))[, 1]), 0); \\ _Amiram Eldar_, Oct 28 2024 %Y A071964 Cf. A000010 (phi), A006530, A068211. %K A071964 easy,nonn %O A071964 1,1 %A A071964 _Benoit Cloitre_, Jun 16 2002