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 A000030 Initial digit of n. (Formerly M0470) 156
 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; text; internal format)
 OFFSET 0,3 COMMENTS For n > 9, n is the concatenation of a(n) and A217657(n). - Reinhard Zumkeller, Oct 10 2012, corrected by M. F. Hasler, Nov 17 2018 Equivalent definition: The initial a(0) = 0 is followed by each digit in S = {1,...,9} once. Thereafter, repeat 10 times each digit in S. Then, repeat 100 times each digit in S, etc. REFERENCES N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS David W. Wilson, Table of n, a(n) for n = 0..10000 A. Cobham, Uniform Tag Sequences, Mathematical Systems Theory, 6 (1972), 164-192. 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 a(n) = k for k*10^j <= n < (k+1)*10^j for some j. - M. F. Hasler, Mar 23 2015 EXAMPLE 23 begins with a 2, so a(23) = 2. MAPLE Ldigit:=proc(n) local v; v:=convert(n, base, 10); v[-1]; end; [seq(Ldigit(n), n=0..200)]; # N. J. A. Sloane, Feb 10 2017 MATHEMATICA Join[{0}, First[IntegerDigits[#]]&/@Range[90]] (* Harvey P. Dale, Mar 01 2011 *) Table[Floor[n/10^(Floor[Log10[n]])], {n, 1, 50}] (* G. C. Greubel, May 16 2017 *) PROG (PARI) a(n)=if(n<10, n, a(n\10)) \\ Mainly for illustration. (PARI) A000030(n)=n\10^logint(n+!n, 10) \\ Twice as fast as a(n)=digits(n)[1]. Before digits() was added in PARI v.2.6.0 (2013), one could use, e.g., Vecsmall(Str(n))[1]-48. - M. F. Hasler, Nov 17 2018 (Haskell) a000030 = until (< 10) (`div` 10) -- Reinhard Zumkeller, Feb 20 2012, Feb 11 2011 (MAGMA) [Intseq(n)[#Intseq(n)]: n in [1..100]]; // Vincenzo Librandi, Nov 17 2018 CROSSREFS Cf. A010879 (final digit of n). Cf. A061681, A130571, A109453, A134010, A052038. Cf. A002993, A089951, A002994, A143464, A098174, A098175, A072543, A072544, A073600, A073601, A037904. - Reinhard Zumkeller, Aug 17 2008 Sequence in context: A052423 A126616 A121042 * A179635 A306354 A216587 Adjacent sequences:  A000027 A000028 A000029 * A000031 A000032 A000033 KEYWORD nonn,base,easy,nice,look AUTHOR STATUS approved

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Last modified October 19 21:08 EDT 2019. Contains 328228 sequences. (Running on oeis4.)