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A004216 a(n) = floor(log_10(n)).

%I A004216 #45 Jul 02 2025 16:01:54
%S A004216 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 A004216 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 A004216 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 A004216 a(n) = floor(log_10(n)).
%H A004216 Reinhard Zumkeller, <a href="/A004216/b004216.txt">Table of n, a(n) for n = 1..10000</a>
%F A004216 a(n) = if n > 9 then a(floor(n/10)) + 1, else 0. - _Reinhard Zumkeller_, Oct 31 2001
%F A004216 a(n) = A055642(n) - 1. - _L. Edson Jeffery_, Jul 09 2014
%F A004216 G.f.: (1/(1 - x))*Sum_{k>=1} x^(10^k). - _Ilya Gutkovskiy_, Jan 08 2017
%t A004216 Table[ Length[ IntegerDigits[n, 10] ] - 1, {n, 105}] (* _Jean-François Alcover_, Jun 10 2013 *)
%t A004216 Table[Floor[Log10[n]], {n, 105}] (* _L. Edson Jeffery_, Jul 09 2014 *)
%o A004216 (Haskell)
%o A004216 a004216 n = if n <= 9 then 0 else 1 + a004216 (n `div` 10)
%o A004216 -- _Reinhard Zumkeller_, Dec 22 2012
%o A004216 (PARI) a(n) = logint(n, 10); \\ _Michel Marcus_, Oct 16 2021
%o A004216 (Python)
%o A004216 def A004216(n): return len(str(n))-1 # _Chai Wah Wu_, May 02 2023
%Y A004216 Cf. A055642.
%K A004216 nonn,easy
%O A004216 1,100
%A A004216 _N. J. A. Sloane_
%E A004216 More terms from _James Sellers_, Sep 19 2000