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 A046043 Autobiographical numbers (or curious numbers): numbers n = x0 x1 x2...x9 such that xi is the number of digits equal to i in n. 10
 1210, 2020, 21200, 3211000, 42101000, 521001000, 6210001000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Better definition: n-digit numbers x_0 x_1 x_2 ... x_{n-1} in base n such that x_i is the number of digits equal to i in the number. There are no such numbers for n<=3 or n=6, two such numbers for n=4, and exactly one such number for n=5 and each n>=7. These numbers form the sequence. - David Callan, Feb 17 2017 Proof of completeness based on: x0 > 0; xi > 2 only if i = 0; for i > 2, xi = 1 if i = x0, xi = 0 otherwise. Enumerated by David Castro (david_castro(AT)retek.com). REFERENCES E. Angelini, "Jeux de suites", in Dossier Pour La Science, pp. 32-35, Volume 59 (Jeux math'), April/June 2008, Paris. M. Gardner, Mathematical Circus, pp. 128; 135 Prob. 7 Alfred A. Knopf NY 1979. Tanya Khovanova, A Story of Storytelling Numbers, Math. Horizons, Sep 2009, 14-17. LINKS Fred Gavin, Letters to the editor, Math. Mag 66 (4) (1993) p 276. Amy Harmon, Beyond 'Hidden Figures': Nurturing New Black and Latino Math Whizzes, New York Times, Feb 17, 2017. Tanya Khovanova, Autobiographical Numbers, arXiv:0803.0270 [math.CO], 2008. K. Uhland, The Ten-Digit Number [Broken link?] EXAMPLE n = 1210 has one 0, two 1's, one 2 and zero 3's and n = "one two one zero". MATHEMATICA isSelfDescribing[n_Integer] := (RotateRight[DigitCount[n]] == PadRight[IntegerDigits[n], 10]); Select[Range[10^10 - 1], isSelfDescribing] (* Martin Ettl, Oct 09 2012 *) (* Warning: This program causes Mathematica to crash! - David Callan, Feb 17 2017 *) CROSSREFS Cf. A138480 (another version). Compare with the "Look-and-Say" version A047841. Sequence in context: A187862 A186864 A135239 * A138480 A047627 A252213 Adjacent sequences:  A046040 A046041 A046042 * A046044 A046045 A046046 KEYWORD nonn,base,nice,fini,full AUTHOR Robert Leduc (leduc(AT)macalester.edu) STATUS approved

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Last modified November 19 08:57 EST 2018. Contains 317348 sequences. (Running on oeis4.)