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%I #11 Jul 01 2015 20:16:57
%S 1,1,2,1,4,1,2,2,0,1,2,1,4,4,6,1,16,1,2,2,4,1,2,6,8,16,2,1,0,1,4,6,0,
%T 0,2,1,0,0,0,1,0,1,2,2,0,1,2,10,0,48,2,1,36,20,6,2,8,1,10,1,16,13,2,2,
%U 0,1,0,2,0,1,2,1,0,0,2,2,0,1,8,74,64,1,16
%N Smallest k such that Sum_{i=0..k} binomial(n,i) is prime, or a(n)=0 if there is no such k.
%C a(n)=0 for n=9,29,33,34,37,38,39,41,45,49,...;
%C records a(n) are 1,2,4,6,16,48,74,...
%C at positions 1,3,5,15,17,50,80,...
%H Peter J. C. Moses, <a href="/A258127/b258127.txt">Table of n, a(n) for n = 1..1000</a>
%F a(n) <= n-1.
%o (PARI) a(n) = {my(k = 0); while(! isprime(sum(i=0, k, binomial(n,i))), k++; if ((k>n) && !isprime(binomial(n,k)), return (0);)); k;} \\ _Michel Marcus_, May 23 2015
%Y Cf. A007318, A258126.
%K nonn
%O 1,3
%A _Vladimir Shevelev_, May 21 2015
%E More terms from _Peter J. C. Moses_, May 21 2015
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