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Search: id:A111284
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| A111284 |
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Number of permutations avoiding the patterns {2143,2341,2413,2431,3142,3241,3412,3421,4123,4213,4231,4321,4132,4312}; number of strong sorting class based on 2143. |
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+0
2
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| 1, 2, 6, 10, 14, 18, 22, 26, 30, 34, 38, 42, 46, 50, 54, 58, 62, 66, 70, 74, 78, 82, 86, 90, 94, 98, 102, 106, 110, 114, 118, 122, 126, 130, 134, 138, 142, 146, 150, 154, 158, 162, 166, 170, 174, 178, 182, 186, 190, 194, 198, 202, 206, 210, 214, 218, 222, 226, 230
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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This sequence might also be called "The Non-Pythagorean integers" since no primitive Pythagorean triangle (PPT) exists containing them. Numbers of form 2n+2 (where n is even) can not be a leg or hypotenuse of PPT [a,b,c]. This excludes all even members of the present sequence. Integers 1 and zero are excluded because they form a 'degenerate triangle' with angles = 0. Compare A125667. - H. Lee Price (tanutuva(AT)rochester.rr.com), Feb 02 2007
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REFERENCES
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M. Albert, R. Aldred, M. Atkinson, C Handley, D. Holton, D. McCaughan, and H. van Ditmarsch, Sorting Classes, Elec. J. of Comb. 12 (2005)
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FORMULA
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a(n)=4n-6; n>=2.
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MATHEMATICA
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Table[If[n == 1, 1, 4n - 6], {n, 60}] (from Robert G. Wilson v (rgwv(at)rgwv.com), Nov 04 2005)
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CROSSREFS
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Cf. A125667.
Sequence in context: A067368 A080456 A068977 this_sequence A130824 A016825 A122905
Adjacent sequences: A111281 A111282 A111283 this_sequence A111285 A111286 A111287
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KEYWORD
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nonn
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AUTHOR
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Len Smiley ( smiley (at) math.uaa.alaska.edu ), Nov 01 2005
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EXTENSIONS
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More terms from Robert G. Wilson v (rgwv(at)rgwv.com), Nov 04 2005
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