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 A117712 Number of pentagonal numbers with n digits. 1
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS Harvey P. Dale, Table of n, a(n) for n = 0..1000 EXAMPLE a(4)= 56 because there are 56 pentagonal numbers with 4 digits. MATHEMATICA nm[n_] := Floor[(1 + Sqrt[1 + 24 n])/6]; Join[{3}, Differences[ Table[nm[10^i], {i, 30}]]] (* Harvey P. Dale, Oct 19 2011 *) CROSSREFS Cf. A000326. Sequence in context: A287901 A354878 A143093 * A106158 A274103 A195995 Adjacent sequences: A117709 A117710 A117711 * A117713 A117714 A117715 KEYWORD base,nonn AUTHOR Luc Stevens (lms022(AT)yahoo.com), Apr 13 2006 EXTENSIONS More terms from Harvey P. Dale, Oct 19 2011 STATUS approved

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Last modified May 30 19:56 EDT 2023. Contains 363061 sequences. (Running on oeis4.)