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A195046
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Concentric 15-gonal numbers.
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5
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0, 1, 15, 31, 60, 91, 135, 181, 240, 301, 375, 451, 540, 631, 735, 841, 960, 1081, 1215, 1351, 1500, 1651, 1815, 1981, 2160, 2341, 2535, 2731, 2940, 3151, 3375, 3601, 3840, 4081, 4335, 4591, 4860, 5131, 5415, 5701, 6000, 6301, 6615, 6931, 7260, 7591
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refs;
listen;
history;
text;
internal format)
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OFFSET
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0,3
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LINKS
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Harvey P. Dale, Table of n, a(n) for n = 0..1000
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FORMULA
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a(n) = 15*n^2/4+11*((-1)^n-1)/8.
a(0)=0, a(1)=1, a(2)=15, a(3)=31, a(n)=2*a(n-1)-2*a(n-3)+a(n-4) [From Harvey P. Dale, Feb 23 2012]
G.f.: -((x*(1+x*(13+x)))/((-1+x)^3*(1+x))) [From Harvey P. Dale, Feb 23 2012]
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MATHEMATICA
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Table[15n^2/4+11((-1)^n-1)/8, {n, 0, 50}] (* or *) LinearRecurrence[ {2, 0, -2, 1}, {0, 1, 15, 31}, 50] (* From Harvey P. Dale, Feb 23 2012 *)
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CROSSREFS
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Column 15 of A195040.
Cf. A032527, A032528, A195045, A195047, A195145, A195146.
Sequence in context: A044457 A132757 A045135 * A102955 A041444 A041446
Adjacent sequences: A195043 A195044 A195045 * A195047 A195048 A195049
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KEYWORD
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nonn,easy
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AUTHOR
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Omar E. Pol, Sep 27 2011
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EXTENSIONS
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Corrected (a(1)=1 added) by Harvey P. Dale, Feb 23 2012
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STATUS
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approved
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