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A007376
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The almost-natural numbers: write n in base 10 and juxtapose digits.
(Formerly M0469)
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65
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1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 0, 1, 1, 1, 2, 1, 3, 1, 4, 1, 5, 1, 6, 1, 7, 1, 8, 1, 9, 2, 0, 2, 1, 2, 2, 2, 3, 2, 4, 2, 5, 2, 6, 2, 7, 2, 8, 2, 9, 3, 0, 3, 1, 3, 2, 3, 3, 3, 4, 3, 5, 3, 6, 3, 7, 3, 8, 3, 9, 4, 0, 4, 1, 4, 2, 4, 3, 4, 4, 4, 5, 4, 6, 4, 7, 4, 8, 4, 9, 5, 0, 5, 1, 5, 2, 5, 3, 5, 4, 5, 5, 5, 6, 5, 7
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Also called the Barbier infinite word.
a(n) = A162711(n,1); A136414(n) = 10*a(n) + a(n+1). [From Reinhard Zumkeller, Jul 11 2009]
a(A031287(n))=0, a(A031288(n))=1, a(A031289(n))=2, a(A031290(n))=3, a(A031291(n))=4, a(A031292(n))=5, a(A031293(n))=6, a(A031294(n))=7, a(A031295(n))=8, a(A031296(n))=9. [Reinhard Zumkeller, Jul 28 2011]
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REFERENCES
| J.-P. Allouche and J. Shallit, Automatic Sequences, Cambridge Univ. Press, 2003, p. 114.
R. Honsberger, Mathematical Chestnuts from Around the World, MAA, 2001; see p. 163.
M. Kraitchik, Mathematical Recreations. Dover, NY, 2nd ed., 1953, p. 49.
48th Putnam Competition, Problem A2, Math. Mag., 61 (1988), 131-134.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
| Robert G. Wilson v, Table of n, a(n) for n=1..100000
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MAPLE
| c:=proc(x, y) local s: s:=proc(m) nops(convert(m, base, 10)) end: if y=0 then 10*x else x*10^s(y)+y: fi end: b:=proc(n) local nn: nn:=convert(n, base, 10):[seq(nn[nops(nn)+1-i], i=1..nops(nn))] end: A:=0: for n from 1 to 75 do A:=c(A, n) od: b(A); # c concatenates 2 numbers while b converts a number to the sequence of its digits - Emeric Deutsch (deutsch(AT)duke.poly.edu), Jul 27 2006
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MATHEMATICA
| Flatten[IntegerDigits/@Range[57]] (* Or *)
a[n_] := Block[{m = 0, d = n, i = 1, l, p}, While[m <= d, l = m; m = 9i*10^(i - 1) + l; i++ ]; i--; p = Mod[d - l, i]; q = Floor[(d - l)/i] + 10^(i - 1); If[p != 0, IntegerDigits[q][[p]], Mod[q - 1, 10]]]; Table[ a[n], {n, 1, 105}]
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PROG
| (Haskell)
import Data.List (unfoldr)
a007376 n = a007376_list !! (n-1)
a007376_list = concatMap (reverse . unfoldr
(\x -> if x == 0 then Nothing else Just $ swap $ divMod x 10)) [1..]
-- Reinhard Zumkeller, Dec 17 2011, Mar 28 2011
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CROSSREFS
| Considered as a sequence of digits, this is the same as the decimal expansion of the Champernowne constant, A033307. See that entry for a formula for a(n), further references, etc.
Cf. A054632, A023103.
For "decimations" see A127050 A127353 A127414 A127508 A127584 A127734 A127794 A127950 A128178 A128211 A128359 A128423 A128475 A128881.
Cf. A193428.
Sequence in context: A169930 A179295 A033307 * A189823 A001073 A076313
Adjacent sequences: A007373 A007374 A007375 * A007377 A007378 A007379
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KEYWORD
| base,easy,nice,nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Robert G. Wilson v (rgwv(AT)rgwv.com)
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