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A117712
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Number of pentagonal numbers with n digits.
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1
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3, 6, 17, 56, 177, 558, 1766, 5583, 17655, 55829, 176550, 558297, 1765493, 5582976, 17654924, 55829769, 176549231, 558297692, 1765492316, 5582976912, 17654923165, 55829769118, 176549231655, 558297691180, 1765492316544, 5582976911806, 17654923165439
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history;
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internal format)
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OFFSET
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0,1
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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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EXAMPLE
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a(4)= 56 because there are 56 pentagonal numbers with 4 digits.
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MATHEMATICA
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nm[n_] := Floor[(1 + Sqrt[1 + 24 n])/6]; Join[{3}, Differences[ Table[nm[10^i], {i, 30}]]] (* Harvey P. Dale, Oct 19 2011 *)
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CROSSREFS
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Cf. A000326.
Sequence in context: A287901 A354878 A143093 * A106158 A274103 A195995
Adjacent sequences: A117709 A117710 A117711 * A117713 A117714 A117715
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KEYWORD
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base,nonn
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AUTHOR
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Luc Stevens (lms022(AT)yahoo.com), Apr 13 2006
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EXTENSIONS
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More terms from Harvey P. Dale, Oct 19 2011
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STATUS
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approved
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