login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A318280 A permutation of the positive integers defined in the comment section such that the sum of the first n terms of the sequence is divisible by n. 0
1, 3, 2, 10, 4, 220, 5, 235, 6, 354, 7, 497, 8, 664, 9, 1143, 11, 79117, 12, 2445932, 13, 87580535, 14, 3572000558, 15, 163703541857, 16, 8336823369072, 17, 467409009871723, 18, 28624087521132434, 19, 1901883146740912949, 20 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Start the sequence at a(1) = 1. For each n, if the sum of the first 2n-1 terms is S(n), then define a(2n+1) to be the smallest positive integer that has not appeared in {a(1), a(2), ..., a(2n-1)}, and a(2n) = a(2n+1)*[(2n+1)^t-1] - S(n), where t is the smallest positive integer that makes a(2n) > a(2n-2) (if n = 1, choose t = 1). [Simplified and corrected by Jianing Song, Oct 04 2019]

This is a sequence of positive integers in which each number occurs exactly once such that for each n = 1,2,3,... the sum of the first n terms of the sequence is divisible by n.

If we always choose the smallest candidate for each a(n), we get A019444. - Jianing Song, Oct 04 2019

Is a(2n-1) = A183301(n)? - Dmitry Kamenetsky, Jul 11 2019 [Answer: No, because a(37) = 21 while A183301(19) = 22. - Jianing Song, Oct 04 2019]

LINKS

Table of n, a(n) for n=1..35.

The IMO Compendium Group, 21st All-Russian Mathematical Olympiad 1995: Grade 10 Problem 3

EXAMPLE

The first term is 1. So S(1) = 1, a(3) = 2.

This gives a(2) = 2*(3^t-1) - 1 = 3, here t = 1. So S(2) = 6, a(5) = 4.

This gives a(4) = 4*(5^t-1) - 6 = 10 > a(2), here t = 1. So S(3) = 20, a(7) = 5.

This gives a(6) = 5*(7^t-1) - 20 = 220 > a(4), here t = 2. So S(4) = 245, a(9) = 6.

...

S(7) = 2025, a(17) = 11, so a(16) = 11*(17^t-1) - 2025 = 1143 > a(14) = 664, here t = 2. [Rewritten by Jianing Song, Oct 04 2019]

CROSSREFS

Cf. A019444.

Sequence in context: A090780 A184174 A277821 * A057977 A063549 A071653

Adjacent sequences:  A318277 A318278 A318279 * A318281 A318282 A318283

KEYWORD

nonn

AUTHOR

Jinyuan Wang, Aug 23 2018

EXTENSIONS

Incorrect definition removed by Jianing Song, Oct 04 2019

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 August 9 11:08 EDT 2020. Contains 336323 sequences. (Running on oeis4.)