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A005528
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Stormer numbers or arc-cotangent irreducible numbers (largest prime factor of n^2 + 1 is >= 2n.
(Formerly M0950)
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8
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1, 2, 4, 5, 6, 9, 10, 11, 12, 14, 15, 16, 19, 20, 22, 23, 24, 25, 26, 27, 28, 29, 33, 34, 35, 36, 37, 39, 40, 42, 44, 45, 48, 49, 51, 52, 53, 54, 56, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 69, 71, 74, 77, 78, 79, 80, 81, 82, 84, 85, 86, 87, 88, 89, 90, 92, 94, 95, 96
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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REFERENCES
| John H. Conway and R. K. Guy, The Book of Numbers, Copernicus Press, p. 246.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
J. Todd, A problem on arc tangent relations, Amer. Math. Monthly, 56 (1949), 517-528.
J. Todd, Table of Arctangents. National Bureau of Standards, Washington, DC, 1951, p. 2.
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LINKS
| T. D. Noe, Table of n, a(n) for n = 1..1000
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MATHEMATICA
| Select[Range[96], FactorInteger[#^2 + 1][[-1, 1]] >= 2 # &] (* From Jean-François Alcover, Apr 11 2011 *)
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CROSSREFS
| Cf. A002312.
Sequence in context: A072726 A153242 A143070 * A050015 A153218 A063656
Adjacent sequences: A005525 A005526 A005527 * A005529 A005530 A005531
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KEYWORD
| nonn,nice,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com) and J. H. Conway (conway(AT)math.princeton.edu)
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