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 A187370 Least odd number k such that (k*2^n+1)*k*2^n + 1 is prime. 5
 1, 3, 1, 5, 9, 3, 21, 3, 1, 11, 13, 5, 27, 27, 7, 5, 27, 3, 27, 41, 13, 11, 49, 5, 69, 83, 61, 47, 9, 21, 3, 3, 45, 35, 21, 21, 3, 3, 7, 39, 9, 3, 27, 51, 73, 35, 27, 33, 27, 125, 103, 255, 27, 63, 207, 171, 153, 27, 3, 105, 147 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS As N increases, it appears that (sum_{k=1..N} a(k)) / (sum_{k=1..N} k) tends to 1.25. LINKS Pierre CAMI, Table of n, a(n) for n = 1..4000 MATHEMATICA Table[k = 1; While[! PrimeQ[(k*2^n + 1)*k*2^n + 1], k = k + 2]; k, {n, 100}] CROSSREFS Cf. A187367, A187368, A187369, A187371. Sequence in context: A128821 A221446 A029723 * A215456 A225855 A201751 Adjacent sequences:  A187367 A187368 A187369 * A187371 A187372 A187373 KEYWORD nonn AUTHOR Pierre CAMI, Mar 09 2011 STATUS approved

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Last modified August 3 14:27 EDT 2021. Contains 346438 sequences. (Running on oeis4.)