A083730 - OEIS

A083730

Greatest prime^2 factor of n, or a(n)=1 for squarefree n.

1, 1, 1, 4, 1, 1, 1, 4, 9, 1, 1, 4, 1, 1, 1, 4, 1, 9, 1, 4, 1, 1, 1, 4, 25, 1, 9, 4, 1, 1, 1, 4, 1, 1, 1, 9, 1, 1, 1, 4, 1, 1, 1, 4, 9, 1, 1, 4, 49, 25, 1, 4, 1, 9, 1, 4, 1, 1, 1, 4, 1, 1, 9, 4, 1, 1, 1, 4, 1, 1, 1, 9, 1, 1, 25, 4, 1, 1, 1, 4, 9, 1, 1, 4, 1, 1, 1, 4, 1, 9, 1, 4, 1, 1, 1, 4, 1, 49, 9

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OFFSET

1,4

COMMENTS

Not multiplicative, for example a(4)*a(9) <> a(36). - R. J. Mathar, Oct 31 2011

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A249740(n)^2. - Amiram Eldar, Feb 11 2021

MATHEMATICA

a[n_] := If[(pos = Position[(f = FactorInteger[n])[[;; , 2]], _?(# >= 2 &)]) == {}, 1, f[[pos[[-1, 1]], 1]]^2]; Array[a, 100] (* Amiram Eldar, Nov 14 2020 *)

PROG

(PARI) a(n)=my(f=factor(n)); forstep(i=#f~, 1, -1, if(f[i, 2]>1, return(f[i, 1]^2))); 1 \\ Charles R Greathouse IV, Jul 23 2017

CROSSREFS

Cf. A006530, A001248, A005117, A013929, A008833, A046028, A249740.

Sequence in context: A350698 A335324 A366245 * A373440 A358272 A008833

Adjacent sequences: A083727 A083728 A083729 * A083731 A083732 A083733

KEYWORD

nonn,easy

AUTHOR

Reinhard Zumkeller, Jun 14 2003

STATUS

approved