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A258569
Smallest prime factors of 4-full numbers, a(1)=1.
6
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, 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, 11, 2, 3, 2, 3, 2, 2, 2, 2, 2, 3, 2, 2, 23, 2, 2, 2, 2
OFFSET
1,2
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 (some terms corrected by Georg Fischer)
FORMULA
a(n) = A020639(A036967(n));
a(A258601(n)) = A000040(n) and a(m) != A000040(n) for m < A258601(n).
MATHEMATICA
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 *)
PROG
(Haskell)
a258569 = a020639 . a036967
(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
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jun 06 2015
STATUS
approved