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 A004216 a(n) =  floor(log_10(n)). 23

%I

%S 0,0,0,0,0,0,0,0,0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,

%T 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,

%U 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,2,2,2,2,2

%N a(n) = floor(log_10(n)).

%H Reinhard Zumkeller, <a href="/A004216/b004216.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = if n > 9 then a(floor(n / 10)) + 1 else 0. - _Reinhard Zumkeller_, Oct 31 2001

%F a(n) = floor(log_10(n)) = A055642(n) - 1. - _L. Edson Jeffery_, Jul 09 2014

%F G.f.: (1/(1 - x))*Sum_{k>=1} x^(10^k). - _Ilya Gutkovskiy_, Jan 08 2017

%t Table[ Length[ IntegerDigits[n, 10] ] - 1, {n, 105}] (* _Jean-François Alcover_, Jun 10 2013 *)

%t Table[Floor[Log10[n]], {n, 105}] (* _L. Edson Jeffery_, Jul 09 2014 *)

%o a004216 n = if n <= 9 then 0 else 1 + a004216 (n `div` 10)

%o -- _Reinhard Zumkeller_, Dec 22 2012

%Y Cf. A055642.

%K nonn

%O 1,100

%A _N. J. A. Sloane_

%E More terms from _James A. Sellers_, Sep 19 2000

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Last modified September 22 14:03 EDT 2020. Contains 337289 sequences. (Running on oeis4.)