%I #25 Feb 11 2021 03:32:04

%S 1,1,1,2,1,1,1,2,3,1,1,2,1,1,1,2,1,3,1,2,1,1,1,2,5,1,3,2,1,1,1,2,1,1,

%T 1,2,1,1,1,2,1,1,1,2,3,1,1,2,7,5,1,2,1,3,1,2,1,1,1,2,1,1,3,2,1,1,1,2,

%U 1,1,1,2,1,1,5,2,1,1,1,2,3,1,1,2,1,1,1,2,1,3,1,2,1,1,1,2,1,7,3,2,1,1,1,2,1,1,1,2,1,1,1,2,1,1,1,2,3,1,1,2

%N The smallest prime whose square divides n, 1 if n is squarefree.

%C A249740 gives the corresponding largest prime.

%C If n belongs to A013929, then a(n)>1. - _Robert G. Wilson v_, Nov 16 2016

%H Antti Karttunen, <a href="/A249739/b249739.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A020639(A003557(n)). - _Amiram Eldar_, Feb 11 2021

%t Table[If[SquareFreeQ@ n, 1, p = 2; While[! Divisible[n, p^2], p = NextPrime@ p]; p], {n, 120}] (* _Michael De Vlieger_, Nov 15 2016 *)

%o (Scheme) (define (A249739 n) (let loop ((n n) (p (A020639 n))) (cond ((= 1 n) n) ((zero? (modulo n (* p p))) p) (else (loop (/ n p) (A020639 (/ n p)))))))

%o (PARI) a(n) = {f = factor(n/core(n)); vsq = select(x->((x%2) == 0), f[,2], 1); if (#vsq, f[vsq[1], 1], 1);} \\ _Michel Marcus_, Mar 11 2017

%Y Cf. A003557, A005117, A013929, A020639, A046027, A249717.

%Y Differs from A071773 and A249740 for the first time at n=36, where a(36) = 2, while A249740(36) = 3 and A071773(36) = 6.

%K nonn

%O 1,4

%A _Antti Karttunen_, Nov 04 2014