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 A078777 a(n) = the least positive integer k such that binomial(2k,k) + k + n is prime, if such k exists; = 0, otherwise. 0
 1, 0, 1, 2, 1, 2, 3, 6, 1, 2, 1, 2, 5, 120, 1, 2, 1, 6, 3, 58, 1, 2, 7, 2, 3, 12, 1, 4, 1, 2, 3, 12, 9, 2, 1, 2, 3, 6, 1, 2, 1, 6, 19, 16, 1, 2, 13, 6, 3, 12, 1, 2, 7, 2, 5, 16, 1, 4, 1, 2, 3, 6, 15, 2, 1, 2, 3, 6, 1, 14, 1, 2, 7, 16, 3, 2, 1, 4, 3, 6, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS The value a(1) = 0 is conjectural. There is no k < 8.5 x 10^3 such that binomial(2k,k)+k+1 is prime. There is no k < 10^8 making binomial(2k,k)+k+1 prime. - Charles R Greathouse IV, May 19 2013 LINKS EXAMPLE k=2 is the least positive integer such that binomial(2k,k) + k + 3 is prime. Hence a(2) = 3. PROG (PARI) a(n) = {k = 1; while(! isprime(binomial(2*k, k) + k + n), k++; if (k % 1000 == 0, print(k)); ); return (k); }  \\ Michel Marcus, May 19 2013 CROSSREFS Sequence in context: A204994 A132405 A057192 * A135938 A079210 A070861 Adjacent sequences:  A078774 A078775 A078776 * A078778 A078779 A078780 KEYWORD nonn,changed AUTHOR Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Jan 09 2003 EXTENSIONS a(0) = 1 prepended to sequence to match offset by Michel Marcus, May 19 2013 STATUS approved

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Last modified May 20 21:27 EDT 2013. Contains 225464 sequences.