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A009005 All natural numbers except 1, 2 and 4. 5
3, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Short legs of Pythagorean triangles.

Also the natural numbers n such that there is an open knight's tour of the 4 X n chessboard. - Sharon Sela (sharonsela(AT)hotmail.com), Jan 02 2002

Also perimeters of integral triangles; equivalently, numbers n = a + b + c, where a + b > c, a + c > b, b + c > a, and a, b, c are integers (necessarily a, b, c, and n are positive). - Rick L. Shepherd, Aug 04 2013

Along with 0, possible scores in rugby union, where points can be scored with a penalty goal or drop goal (3 points), try (5 points) and converted try (7 points). - Charles R Greathouse IV, Sep 10 2016

LINKS

Table of n, a(n) for n=1..74.

IBM Ponder This, 2001

Index entries for linear recurrences with constant coefficients, signature (2,-1).

FORMULA

O.g.f.: x(3-x-x^2)/(1-x)^2. a(n)=A009056(n), n>1. - R. J. Mathar, May 26 2008

PROG

(PARI) a(n)=n+4-(n==1) \\ Charles R Greathouse IV, Sep 02 2011

CROSSREFS

Sequence in context: A009004 A005527 A285173 * A138884 A008521 A299489

Adjacent sequences:  A009002 A009003 A009004 * A009006 A009007 A009008

KEYWORD

nonn,easy

AUTHOR

David W. Wilson

STATUS

approved

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Last modified October 20 11:13 EDT 2018. Contains 316379 sequences. (Running on oeis4.)