Search: id:A000030
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%I A000030 M0470
%S A000030 0,1,2,3,4,5,6,7,8,9,1,1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2,2,
%T A000030 2,3,3,3,3,3,3,3,3,3,3,4,4,4,4,4,4,4,4,4,4,5,5,5,5,5,5,5,
%U A000030 5,5,5,6,6,6,6,6,6,6,6,6,6,7,7,7,7,7,7,7,7,7,7,8,8,8,8,8
%N A000030 Initial digit of n.
%D A000030 A. Cobham, Uniform Tag Sequences, Mathematical Systems Theory, 6 (1972), 
               164-192.
%D A000030 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%H A000030 David W. Wilson, <a href="b000030.txt">Table of n, a(n) for n = 0..10000</
               a>
%F A000030 a(n) = [n / 10^([log_10(n)])] where [] denotes floor and log_10(n) is 
               the logarithm is base 10. - Dan Fux (dan.fux(AT)OpenGaia.com or danfux(AT)OpenGaia.com), 
               Apr 07 2001
%e A000030 23 begins with a 2, so a(23) = 2.
%t A000030 a[n_] := First[IntegerDigits[n]]
%o A000030 (PARI) a(n)=if(n<1,0,if(n<10,n,a(n\10)))
%Y A000030 Cf. A061681, A130571, A109453, A134010.
%Y A000030 A002993, A089951, A002994, A143464, A098174, A098175, A072543, A072544, 
               A073600, A073601, A037904. [From Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), 
               Aug 17 2008]
%Y A000030 Sequence in context: A052423 A126616 A121042 this_sequence A134777 A004427 
               A113230
%Y A000030 Adjacent sequences: A000027 A000028 A000029 this_sequence A000031 A000032 
               A000033
%K A000030 nonn,base,easy,nice
%O A000030 0,3
%A A000030 N. J. A. Sloane (njas(AT)research.att.com), Simon Plouffe (simon.plouffe(AT)gmail.com)

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