cp's OEIS Frontend

A258569 Smallest prime factors of 4-full numbers, a(1)=1.

%I A258569 #27 Sep 09 2024 02:41:21
%S A258569 1,2,2,2,3,2,3,2,2,5,3,2,2,2,3,7,2,5,2,2,2,3,2,2,2,2,2,11,2,5,2,7,3,2,
%T A258569 2,2,13,2,2,2,2,2,2,2,2,3,3,2,2,2,2,5,2,2,17,2,2,2,7,2,19,2,2,3,2,2,
%U A258569 11,2,3,2,3,2,2,2,2,2,3,2,2,23,2,2,2,2
%N A258569 Smallest prime factors of 4-full numbers, a(1)=1.
%H A258569 Reinhard Zumkeller, <a href="/A258569/b258569.txt">Table of n, a(n) for n = 1..10000</a> (some terms corrected by Georg Fischer)
%F A258569 a(n) = A020639(A036967(n));
%F A258569 a(A258601(n)) = A000040(n) and a(m) != A000040(n) for m < A258601(n).
%t A258569 Reap[Sow[1]; Do[f = FactorInteger[k]; If[Min[f[[All, 2]]] >= 4, Sow[f[[1, 1]]]], {k, 2, 10^6}]][[2, 1]] (* _Jean-François Alcover_, Sep 29 2020 *)
%o A258569 (Haskell)
%o A258569 a258569 = a020639 . a036967
%o A258569 (PARI) lista(kmax) = {my(f); print1(1, ", "); for(k = 2, kmax, f = factor(k); if(vecmin(f[, 2]) > 3, print1(f[1, 1], ", ")));} \\ _Amiram Eldar_, Sep 09 2024
%Y A258569 Cf. A036967, A020639, A258601, A258567, A258568, A258570, A258571.
%K A258569 nonn
%O A258569 1,2
%A A258569 _Reinhard Zumkeller_, Jun 06 2015