A117712 Number of pentagonal numbers with n digits.

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

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 A377184

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