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A007923 Lengths increase by 1, digits cycle through positive digits. 7
1, 23, 456, 7891, 23456, 789123, 4567891, 23456789, 123456789, 1234567891, 23456789123, 456789123456, 7891234567891, 23456789123456, 789123456789123, 4567891234567891, 23456789123456789, 123456789123456789 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

C. Ashbacher, Some Problems Concerning the Smarandache Deconstructive Sequence, J. Recreational Mathematics, Vol. 29, No. 2, pages 82-84.

K. Atanassov, On the 4th Smarandache Problem, Notes on Number Theory and Discrete Mathematics, Sophia, Bulgaria, Vol. 5 (1999), No. 1, 33-35.

LINKS

John Cerkan, Table of n, a(n) for n = 1..994

K. Atanassov, On Some of Smarandache's Problems

F. Smarandache, Only Problems, Not Solutions!

Eric Weisstein's World of Mathematics, Smarandache Sequences

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

a(n) = floor(10^(n*(n+1)/2)*123456789/999999999) - 10^n*floor(10^(n*(n-1)/2)*123456789/999999999). - Néstor Jofré, Jun 03 2017

PROG

(PARI) a(n)=my(m=(n*(n+1)/2-1)%9); sum(k=0, n-1, 10^k*((m-k)%9+1))

CROSSREFS

Cf. A001369, A007924, A050234, A066547.

Sequence in context: A062273 A066547 A001369 * A080479 A053067 A036906

Adjacent sequences:  A007920 A007921 A007922 * A007924 A007925 A007926

KEYWORD

nonn,easy,base

AUTHOR

R. Muller

STATUS

approved

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Last modified November 20 14:54 EST 2019. Contains 329337 sequences. (Running on oeis4.)