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A009994 Numbers with digits in nondecreasing order. 28
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 14, 15, 16, 17, 18, 19, 22, 23, 24, 25, 26, 27, 28, 29, 33, 34, 35, 36, 37, 38, 39, 44, 45, 46, 47, 48, 49, 55, 56, 57, 58, 59, 66, 67, 68, 69, 77, 78, 79, 88, 89, 99, 111, 112, 113, 114, 115, 116, 117, 118, 119, 122 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Record values and occurrences of A004185. - Reinhard Zumkeller, Dec 05 2009

A193581(a(n)) = 0. - Reinhard Zumkeller, Aug 10 2011

This sequence was used by the U.S. Bureau of the Census in the mid-1950s to numerically code the alphabetical list of counties within a state (with some modifications for Texas). The 3-digit code has a "self-policing element" built into it and "was fairly effective in detecting the transposition of 2 digits." (Hanna 1959). - Randy A. Becker, Dec 11 2017

REFERENCES

Amarnath Murthy and Robert J. Clarke, Some Properties of Staircase sequence, Mathematics & Informatics Quarterly, Volume 11, No. 4, November 2001.

Hanna, Frank A. The Compilation of Manufacturing Statistics. U.S. Department of Commerce, Bureau of the Census, 1959.

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..1000

D. Applegate, M. LeBrun, N. J. A. Sloane, Dismal Arithmetic, J. Int. Seq. 14 (2011) # 11.9.8.

Eric Weisstein's World of Mathematics, Digit.

Index entries for 10-automatic sequences.

FORMULA

a(n) >> exp(n^(1/10)). - Charles R Greathouse IV, Mar 15 2014

MATHEMATICA

Select[Range[0, 125], LessEqual@@IntegerDigits[#]&] (* Ray Chandler, Oct 25 2011 *)

PROG

(Haskell)

import Data.Set (fromList, deleteFindMin, insert)

a009994 n = a009994_list !! n

a009994_list = 0 : f (fromList [1..9]) where

   f s = m : f (foldl (flip insert) s' $ map (10*m +) [m `mod` 10 ..9])

         where (m, s') = deleteFindMin s

-- Reinhard Zumkeller, Aug 10 2011

(PARI) is(n)=n=digits(n); n==vecsort(n) \\ Charles R Greathouse IV, Dec 03 2013

(Python)

from itertools import combinations_with_replacement

def A009994generator():

    yield 0

    l = 1

    while True:

        for i in combinations_with_replacement('123456789', l):

            yield int(''.join(i))

        l += 1 # Chai Wah Wu, Nov 11 2015

CROSSREFS

Apart from the first term, a subsequence of A052382. A254143 is a subsequence.

Cf. A152054, A036839.

Sequence in context: A131058 A032857 A072544 * A239016 A102827 A190221

Adjacent sequences:  A009991 A009992 A009993 * A009995 A009996 A009997

KEYWORD

nonn,base,look

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified April 21 06:50 EDT 2018. Contains 302832 sequences. (Running on oeis4.)