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A051943
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Truncated triangular pyramid numbers: a(n) = Sum_{k=9..n} (k*(k+1)/2 - 45).
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1
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0, 10, 31, 64, 110, 170, 245, 336, 444, 570, 715, 880, 1066, 1274, 1505, 1760, 2040, 2346, 2679, 3040, 3430, 3850, 4301, 4784, 5300, 5850, 6435, 7056, 7714, 8410, 9145, 9920, 10736, 11594, 12495, 13440, 14430, 15466, 16549, 17680, 18860, 20090
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OFFSET
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9,2
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LINKS
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FORMULA
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a(n) = (n+20)*(n-8)*(n-9)/6.
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MATHEMATICA
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LinearRecurrence[{4, -6, 4, -1}, {0, 10, 31, 64}, 50] (* Vincenzo Librandi, Jun 18 2012 *)
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PROG
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(Magma) I:=[0, 10, 31, 64]; [n le 4 select I[n] else 4*Self(n-1)-6*Self(n-2)+4*Self(n-3)-Self(n-4): n in [1..45]]; // Vincenzo Librandi, Jun 18 2012
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CROSSREFS
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KEYWORD
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easy,nice,nonn
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AUTHOR
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Klaus Strassburger (strass(AT)ddfi.uni-duesseldorf.de), Dec 21 1999
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STATUS
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approved
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