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 A229027 #25 Nov 03 2024 18:55:09
%S A229027 4,9,18,25,49,50,75,98,121,147,150,169,242,245,289,294,338,361,363,
%T A229027 490,507,529,578,605,722,726,735,841,845,847,867,961,1014,1058,1083,
%U A229027 1183,1210,1369,1445,1470,1587,1681,1682,1690,1694,1734,1805,1815,1849,1859
%N A229027 Numbers k such that k/rad(k) equals the greatest prime dividing k.
%C A229027 Numbers k such that k/A007947(k) = A006530(k) where A007947 is the product of the distinct prime factors of k and A006530 is the greatest prime dividing k.
%C A229027 The numbers of the form p^2 with p prime, or of the form p_1*p_2*...*p_k*p^2 with p_i primes < p prime are in the sequence.
%C A229027 All these numbers are round numbers (their greatest prime factor is <= their square root). - _Emmanuel Vantieghem_, Feb 22 2017
%H A229027 Harvey P. Dale, <a href="/A229027/b229027.txt">Table of n, a(n) for n = 1..1000</a>
%p A229027 with(numtheory) :for n from 2 to 2000 do:x:=factorset(n):n1:=nops(x): p:= product('x[i]', 'i'=1..n1):m:=n/p:if m=x[n1] then printf(`%d, `,n):else fi:od:
%t A229027 rad[n_]:=Times@@(First@#&/@FactorInteger@n);Select[Range[2,2000],FactorInteger[#][[-1,1]]==#/rad[#]&]
%t A229027 gpQ[n_]:=Module[{pf=Transpose[FactorInteger[n]][[1]]},n/Times@@pf == Last[ pf]]; Select[Range[2,2000],gpQ] (* _Harvey P. Dale_, Aug 16 2014 *)
%o A229027 (PARI) isok(n) = my(f = factor(n)); n/factorback(f[, 1]) == f[#f~, 1]; \\ _Michel Marcus_, Aug 16 2014
%Y A229027 Cf. A007947, A006530, A228957.
%K A229027 nonn
%O A229027 1,1
%A A229027 _Michel Lagneau_, Sep 11 2013