OFFSET
1,2
COMMENTS
Most significant prime factor of n: If n = (p_1^e_1)(p_2^e_2)(p_3^e_3)... and max(p_1^e_1,p_2^e_2,...) = p_k^e_k then a(n) = p_k.
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..65537
FORMULA
a(n*a(n)) = a(n). - Sam Alexander, Dec 15 2003
EXAMPLE
a(6) = a(2*3) = 3 because 3^1 > 2^1;
a(36) = a((2^2)(3^2)) = 3 because 3^2 > 2^2;
a(12) = a((2^2)*3) = 2 because 2^2 > 3^1.
MATHEMATICA
f[n_] := Sort[ {#[[1]]^#[[2]], #[[1]]} & /@ FactorInteger@ n][[ -1, 2]]; Array[f, 85] (* Robert G. Wilson v, Nov 05 2007 *)
a[n_] := MaximalBy[FactorInteger[n], Power @@ # &][[1, 1]];
Array[a, 85] (* Jean-François Alcover, Jun 27 2019 *)
PROG
(PARI) A088387(n) = if(1==n, 1, my(f=factor(n), p=0); isprimepower(vecmax(vector(#f[, 1], i, f[i, 1]^f[i, 2])), &p); (p)); \\ Antti Karttunen, Jul 22 2018
(Python)
from sympy import factorint
def A088387(n): return max(((p**e, p) for p, e in factorint(n).items()), default=(0, 1))[1] # Chai Wah Wu, Apr 17 2023
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Reinhard Zumkeller, Sep 28 2003
EXTENSIONS
More terms from Ray Chandler, Dec 20 2003
Edited by N. J. A. Sloane at the suggestion of Stefan Steinerberger, Nov 04 2007
STATUS
approved