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 A258127 Smallest k such that Sum_{i=0..k} binomial(n,i) is prime, or a(n)=0 if there is no such k. 4
 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, 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, 0, 1, 0, 2, 0, 1, 2, 1, 0, 0, 2, 2, 0, 1, 8, 74, 64, 1, 16 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS a(n)=0 for n=9,29,33,34,37,38,39,41,45,49,...; records a(n) are  1,2,4,6,16,48,74,... at positions 1,3,5,15,17,50,80,... LINKS Peter J. C. Moses, Table of n, a(n) for n = 1..1000 FORMULA a(n) <= n-1. PROG (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 CROSSREFS Cf. A007318, A258126. Sequence in context: A100762 A059147 A091891 * A181982 A070194 A323300 Adjacent sequences:  A258124 A258125 A258126 * A258128 A258129 A258130 KEYWORD nonn AUTHOR Vladimir Shevelev, May 21 2015 EXTENSIONS More terms from Peter J. C. Moses, May 21 2015 STATUS approved

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Last modified June 12 14:45 EDT 2021. Contains 344957 sequences. (Running on oeis4.)