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A180847
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a(n) = (27^n-4^n)/23.
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6
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0, 1, 31, 853, 23095, 623821, 16844191, 454797253, 12279542215, 331547705341, 8951788306351, 241698285320053, 6525853707835735, 176198050128342061, 4757347353532344511, 128448378545641737253, 3468106220733400647655
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OFFSET
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0,3
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COMMENTS
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The a(n+1) appear in several triangle sums of Nicomachus' table A036561, i.e Ze1(2*n), Ze1(2*n+1)/2; Ze4(3*n), Ze4(3*n+1)/3 and Ze4(3*n+2)/9. See A180662 for information about these zebra and other chess sums.
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LINKS
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FORMULA
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a(n) = (27^n-4^n)/23.
G.f.: x/((27*x-1)*(4*x-1)).
a(0)=0, a(1)=1, a(n)=31*a(n-1)-108*a(n-2). [From Harvey P. Dale, Sep 01 2011]
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MATHEMATICA
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Table[(27^n-4^n)/23, {n, 0, 20}] (* or *) LinearRecurrence[{31, -108}, {0, 1}, 20] (* Harvey P. Dale, Sep 01 2011 *)
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PROG
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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