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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A217789 Least difference between 2 palindromic numbers of length n. 1
1, 11, 10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

In his video, Fields medallist Villani asks about the number of palindromes of length n (cf. A050683 and A070252), and the minimal difference among any two of these (this sequence). Except for the 1 and 3-digits case (where e.g. 111-101=10), the minimal difference of 11 appears as 20...02 - 19...91 and similar patterns (1st and last digits increased by 1,...,7). - M. F. Hasler, Mar 25 2013

Also, continued fraction expansion of (2695-5*sqrt(5))/2462. [Bruno Berselli, Mar 25 2013]

LINKS

Table of n, a(n) for n=1..65.

Cédric Villani, Les défis mathématiques du Monde, épisode 1 : les palindromes

FORMULA

G.f.: x*(1+10*x-x^2+x^3)/(1-x). [Bruno Berselli, Mar 25 2013]

EXAMPLE

a(1)=1 for instance 8-7.

a(2)=11 for instance 22-11.

a(3)=10 for instance 111-101.

a(n)=11 for n >= 4, for instance 2002-1991, resp. generalization to n digits (cf. comment).

PROG

(PARI) A217789(n)=11-(n==3)-(n==1)*10  \\ [M. F. Hasler, Mar 25 2013]

CROSSREFS

Cf. A050683, A070252.

Sequence in context: A059941 A086100 A182782 * A004283 A106421 A019329

Adjacent sequences:  A217786 A217787 A217788 * A217790 A217791 A217792

KEYWORD

nonn,easy,base

AUTHOR

Michel Marcus, Mar 25 2013

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 October 19 03:08 EDT 2019. Contains 328211 sequences. (Running on oeis4.)