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Search: id:A000030
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| A000030 |
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Initial digit of n.
(Formerly M0470)
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+0
73
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| 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, 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, 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
(list; graph; listen)
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OFFSET
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0,3
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REFERENCES
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A. Cobham, Uniform Tag Sequences, Mathematical Systems Theory, 6 (1972), 164-192.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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David W. Wilson, Table of n, a(n) for n = 0..10000
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FORMULA
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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
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EXAMPLE
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23 begins with a 2, so a(23) = 2.
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MATHEMATICA
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a[n_] := First[IntegerDigits[n]]
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PROGRAM
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(PARI) a(n)=if(n<1, 0, if(n<10, n, a(n\10)))
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CROSSREFS
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Cf. A061681, A130571, A109453, A134010.
A002993, A089951, A002994, A143464, A098174, A098175, A072543, A072544, A073600, A073601, A037904. [From Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Aug 17 2008]
Sequence in context: A052423 A126616 A121042 this_sequence A134777 A004427 A113230
Adjacent sequences: A000027 A000028 A000029 this_sequence A000031 A000032 A000033
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KEYWORD
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nonn,base,easy,nice
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), Simon Plouffe (simon.plouffe(AT)gmail.com)
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