login
This site is supported by donations to The OEIS Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 15 09:05 EST 2019. Contains 329995 sequences. (Running on oeis4.)