This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A213609 #6 Jun 16 2012 06:36:02
%S A213609 1,2,4,6,8,11,15,16,18,20,0,28,29,33,38,42,45,48,53,54,60,64,66,67,75,
%T A213609 77,80,86,91,92,100,102,104,109,111,110,127,0,128,133,140,144,151,154,
%U A213609 153,160,165,170,171,178,0,189,190,192,198,202,209,210,220,225
%N A213609 Smallest number k such that the number of distinct prime divisors of binomial(2k,k) equals n, otherwise 0.
%C A213609 a(A071853(n)) = 0.
%H A213609 Olivier Gérard, <a href="/A213609/b213609.txt">Table of n, a(n) for n = 1..1000</a>
%e A213609 a(3) = 4 because binomial(2*4,4) = 70 with 3 distinct prime divisors {2, 5, 7}.
%p A213609 with(numtheory): for n from 1 to 100 do:ii:=0: for k from 1 to 500 while(ii=0) do:x:=binomial(2*k,k):y:=factorset(x): n1:=nops(y):if n1=n then ii:=1:printf(`%d, `,k):else fi:od:if ii=0 then printf(`%d, `,0):else fi:od:
%Y A213609 Cf. A067434, A071853.
%K A213609 nonn
%O A213609 1,2
%A A213609 _Michel Lagneau_, Jun 16 2012