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A007923
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Lengths increase by 1, digits cycle through positive digits.
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3
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1, 23, 456, 7891, 23456, 789123, 4567891, 23456789, 123456789, 1234567891, 23456789123, 456789123456, 7891234567891, 23456789123456, 789123456789123, 4567891234567891, 23456789123456789, 123456789123456789
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Also called Smarandache deconstructive sequence.
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REFERENCES
| C. Ashbacher, Some Problems Concerning the Smarandache Deconstructive Sequence, J. Recreational Mathematics, Vol. 29, No. 2, pages 82-84.
K. Atanassov, On the 4-th Smarandache Problem, Notes on Number Theory and Discrete Mathematics, Sophia, Bulgaria, Vol. 5 (1999), No. 1, 33-35.
K. Atanassov, On Some of Smarandache Problems, American Research Press, 1999, 16-21.
F. Smarandache, Only Problems, not Solutions!, Xiquan Publ., Phoenix-Chicago, 1993.
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LINKS
| M. L. Perez et al., eds., Smarandache Notions Journal
Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.
F. Smarandache, Only Problems, Not Solutions!
K. Atanassov, On Some of Smarandache's Problems
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FORMULA
| a(n) = (10^9+1) a(n-9) - 10^9 a(n-18), n>=18 (corrected by Michael Somos, Sep 28, 2002).
a(n) = Sum_{i=1..n} ((n*(n-1)/2+i-1 mod 9)+1)*10^(n-i). - Vedran Glisic, Apr 08 2011
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PROG
| (PARI) a(n)=local(m); m=(n*(n+1)/2-1)%9+1; sum(k=0, n-1, 10^k*((m-k-1)%9+1))
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CROSSREFS
| Cf. A050234, A007924.
Sequence in context: A062273 A066547 A001369 * A080479 A053067 A036906
Adjacent sequences: A007920 A007921 A007922 * A007924 A007925 A007926
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KEYWORD
| nonn,easy,base
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AUTHOR
| R. Muller
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