cp's OEIS Frontend

A080215 Binomial(greatest prime factor of n, smallest odd prime factor of n).

%I A080215 #11 Dec 02 2021 13:02:23
%S A080215 1,2,1,2,1,1,1,2,1,1,1,1,1,1,10,2,1,1,1,1,35,1,1,1,1,1,1,1,1,10,1,2,
%T A080215 165,1,21,1,1,1,286,1,1,35,1,1,10,1,1,1,1,1,680,1,1,1,462,1,969,1,1,
%U A080215 10,1,1,35,2,1287,165,1,1,1771,21,1,1,1,1,10,1,330,286,1,1,1,1,1,35
%N A080215 Binomial(greatest prime factor of n, smallest odd prime factor of n).
%H A080215 Antti Karttunen, <a href="/A080215/b080215.txt">Table of n, a(n) for n = 1..16384</a>
%F A080215 a(n) = binomial(A006530(n), A078701(n)). - _Antti Karttunen_, Dec 23 2018
%t A080215 a[n_] := With[{f = Select[FactorInteger[n], #[[1]] != 2&]}, If[f == {}, 2, Binomial[f[[-1, 1]], f[[1, 1]]]]];
%t A080215 Array[a, 100] (* _Jean-François Alcover_, Dec 02 2021 *)
%o A080215 (PARI) A080215(n) = if(1==n,n,my(f = factor(n)[, 1], v = select(x->((x%2)==1), f)); binomial(f[#f], if(#v, vecmin(v), 1))); \\ _Antti Karttunen_, Dec 23 2018
%Y A080215 Cf. A006530, A078701, A080214, A080212.
%K A080215 nonn
%O A080215 1,2
%A A080215 _Reinhard Zumkeller_, Feb 06 2003