cp's OEIS Frontend

A271321 Smallest prime factor of the n-th n-gonal number (A060354).

%I A271321 #11 Feb 26 2022 15:17:13
%S A271321 2,2,2,5,2,2,2,3,2,2,2,13,2,2,2,11,2,2,2,3,2,2,2,5,2,2,2,29,2,2,2,3,2,
%T A271321 2,2,37,2,2,2,11,2,2,2,3,2,2,2,7,2,2,2,53,2,2,2,3,2,2,2,7,2,2,2,5,2,2,
%U A271321 2,3,2,2,2,73,2,2,2,7,2,2,2,3,2,2,2,5
%N A271321 Smallest prime factor of the n-th n-gonal number (A060354).
%H A271321 Colin Barker, <a href="/A271321/b271321.txt">Table of n, a(n) for n = 2..1000</a>
%F A271321 a(n) = A020639(A060354(n)).
%e A271321 a(5) = 5 because A060354(5) = 35 = 5 * 7.
%t A271321 Table[FactorInteger[PolygonalNumber[n,n]][[1,1]],{n,2,90}] (* _Harvey P. Dale_, Feb 26 2022 *)
%o A271321 (PARI)
%o A271321 pg(m, n) = (n^2*(m-2)-n*(m-4))/2 \\ n-th m-gonal number
%o A271321 spf(m) = factorint(m)[1, 1] \\ Smallest prime factor
%o A271321 a(n) = spf(pg(n, n))
%o A271321 vector(100, n, n++; a(n))
%Y A271321 Cf. A020639, A060354, A271319, A271320, A271322.
%K A271321 nonn
%O A271321 2,1
%A A271321 _Colin Barker_, Apr 04 2016