A071964 Numbers k such that k = Gpf(k) * Gpf(phi(k)) where Gpf(k) = A006530(k) is the greatest prime factor of k.
4, 6, 9, 10, 21, 25, 34, 39, 49, 55, 57, 111, 121, 155, 169, 203, 205, 219, 253, 289, 291, 301, 305, 327, 361, 489, 497, 505, 514, 529, 579, 689, 737, 755, 791, 841, 889, 905, 961, 979, 1027, 1081, 1205, 1255, 1299, 1355, 1369, 1379, 1461, 1477, 1681, 1703
Offset: 1
Links
- Amiram Eldar, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
Select[Range[1800],FactorInteger[#][[-1,1]]FactorInteger[EulerPhi[#]][[-1,1]] == #&] (* Harvey P. Dale, Mar 25 2023 *)
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PARI
for(n=1,3000,if(vecmax(component(factor(n),1))*vecmax(component(factor(eulerphi(n)),1))==n,print1(n,",")))
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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