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A129252 Smallest prime factor p of n such that p^p is a divisor of n, a(n)=1 if no such factor exists. 3
1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 3, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 3, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 3, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

a(n) = 1 iff A129251(n) = 0, a(A048103(n)) = 1.

LINKS

R. Zumkeller, Table of n, a(n) for n = 1..10000

EXAMPLE

For n = 108 = 2^2 * 3^3, it is 2 that is the smallest prime factor p satisfying p^p | 108, thus a(108) = 2.

MATHEMATICA

Array[If[IntegerQ@ #, #, 1] &@ First@ SelectFirst[FactorInteger[#], #1 <= #2 & @@ # &] &, 120] (* Michael De Vlieger, Oct 01 2019 *)

PROG

(PARI) A129252(n) = { my(f = factor(n)); for(k=1, #f~, if(f[k, 2]>=f[k, 1], return(f[k, 1]))); (1); }; \\ Antti Karttunen, Oct 01 2019

CROSSREFS

Cf. A020639, A008578, A051674.

Differs from A327936 for the first time at n=108.

Sequence in context: A069291 A268238 A081117 * A327936 A022929 A307706

Adjacent sequences:  A129249 A129250 A129251 * A129253 A129254 A129255

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Apr 07 2007

EXTENSIONS

Data section extended to a(120) by Antti Karttunen, Oct 01 2019

STATUS

approved

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Last modified November 17 16:08 EST 2019. Contains 329241 sequences. (Running on oeis4.)