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A000030
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Initial digit of n.
(Formerly M0470)
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87
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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; refs; listen; history; internal format)
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OFFSET
| 0,3
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REFERENCES
| 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
| David W. Wilson, Table of n, a(n) for n = 0..10000
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FORMULA
| 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
| 23 begins with a 2, so a(23) = 2.
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MATHEMATICA
| First[IntegerDigits[#]]&/@Range[90] (* From Harvey P. Dale, Mar 1 2011 *)
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PROG
| (PARI) a(n)=if(n<1, 0, if(n<10, n, a(n\10)))
(Haskell)
import Data.Char (digitToInt)
a000030 n = (digitToInt . head . show) n
-- Reinhard Zumkeller Feb 11 2011
(PARI) A000030(n)=Vecsmall(Str(n))[1]-48 \\ - M. F. Hasler, Jun 19 2011
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CROSSREFS
| Cf. A061681, A130571, A109453, A134010, A052038.
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 * A179635 A174210 A134777
Adjacent sequences: A000027 A000028 A000029 * A000031 A000032 A000033
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KEYWORD
| nonn,base,easy,nice
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Simon Plouffe (simon.plouffe(AT)gmail.com)
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