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A000030 Initial digit of n.
(Formerly M0470)
141
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

n is the concatenation of a(n) and A217657(n). - Reinhard Zumkeller, Oct 10 2012

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<1, 0, if(n<10, n, a(n\10)))

(Haskell)

a000030 = until (< 10) (`div` 10)

-- Reinhard Zumkeller, Feb 20 2012, Feb 11 2011

(PARI) A000030(n)=Vecsmall(Str(n))[1]-48  \\ M. F. Hasler, Jun 19 2011

(PARI) A000030(n)=digits(n)[1]  \\ M. F. Hasler, Mar 23 2015

CROSSREFS

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 A216587 A174210

Adjacent sequences:  A000027 A000028 A000029 * A000031 A000032 A000033

KEYWORD

nonn,base,easy,nice,look

AUTHOR

N. J. A. Sloane, Simon Plouffe

STATUS

approved

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Last modified September 24 18:54 EDT 2017. Contains 292433 sequences.