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%I #7 Nov 21 2013 12:48:57
%S 3,6,17,56,177,558,1766,5583,17655,55829,176550,558297,1765493,
%T 5582976,17654924,55829769,176549231,558297692,1765492316,5582976912,
%U 17654923165,55829769118,176549231655,558297691180,1765492316544,5582976911806,17654923165439
%N Number of pentagonal numbers with n digits.
%H Harvey P. Dale, <a href="/A117712/b117712.txt">Table of n, a(n) for n = 0..1000</a>
%e a(4)= 56 because there are 56 pentagonal numbers with 4 digits.
%t nm[n_] := Floor[(1 + Sqrt[1 + 24 n])/6]; Join[{3}, Differences[ Table[nm[10^i], {i,30}]]] (* _Harvey P. Dale_, Oct 19 2011 *)
%Y Cf. A000326.
%K base,nonn
%O 0,1
%A Luc Stevens (lms022(AT)yahoo.com), Apr 13 2006
%E More terms from Harvey P. Dale, Oct 19 2011
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