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A005528 Stormer numbers or arc-cotangent irreducible numbers (largest prime factor of n^2 + 1 is >= 2n.
(Formerly M0950)
8
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; text; internal format)
OFFSET

1,2

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.

LINKS

T. D. Noe, Table of n, a(n) for n = 1..1000

MATHEMATICA

Select[Range[96], FactorInteger[#^2 + 1][[-1, 1]] >= 2 # &] (* Jean-Fran├žois Alcover, Apr 11 2011 *)

CROSSREFS

Cf. A002312.

Sequence in context: A153242 A143070 A206926 * A211030 A050015 A153218

Adjacent sequences:  A005525 A005526 A005527 * A005529 A005530 A005531

KEYWORD

nonn,nice,easy

AUTHOR

N. J. A. Sloane and J. H. Conway

STATUS

approved

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Last modified April 24 01:35 EDT 2014. Contains 240947 sequences.