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Search: id:A130205
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| A130205 |
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a(n)=n^2-a(n-1)-a(n-2). |
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+0
2
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| 1, 2, 6, 8, 11, 17, 21, 26, 34, 40, 47, 57, 65, 74, 86, 96, 107, 121, 133, 146, 162, 176, 191, 209, 225, 242, 262, 280, 299, 321, 341, 362, 386, 408, 431, 457, 481, 506, 534, 560, 587, 617, 645, 674, 706, 736, 767, 801, 833, 866, 902, 936, 971, 1009, 1045, 1082
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Any three consecutive terms sum up to a perfect square. First 9 terms coincide with A076991.
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FORMULA
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a(1)=1, a(2)=2; n>2: a(n)=n^2-a(n-1)-a(n-2).
G.f.: x*(1+3*x^2-3*x^3+x^4)/(1+x+x^2)/(1-x)^3 [From Maksym Voznyy (voznyy(AT)mail.ru), Jul 27 2009]
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EXAMPLE
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1+2+6=3^2, 2+6+8=4^2, 6+8+11=5^2.
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MATHEMATICA
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a[1]=1; a[2]=2; a[n_]:=a[n]=n^2-a[n-1]-a[n-2]; Table[a[n], {n, 100}]
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CROSSREFS
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Cf. A076991, A130206.
Sequence in context: A079418 A136496 A076991 this_sequence A054067 A064212 A056906
Adjacent sequences: A130202 A130203 A130204 this_sequence A130206 A130207 A130208
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KEYWORD
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nonn
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AUTHOR
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Zak Seidov (zakseidov(AT)yahoo.com), May 16 2007
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EXTENSIONS
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G.f. proposed by Maksym Voznyy checked and corrected by R. J. Mathar, Sep 16 2009.
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