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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A140516 For definition see comments lines. 0
1, 3, 6, 8, 9, 13, 16, 17, 19, 20, 21, 26, 31, 32, 36, 42, 43, 45, 49, 50, 52, 53, 54, 58, 62, 65, 66, 67, 71, 78, 80, 82, 85, 87, 89, 90, 97, 98, 103, 106, 108, 112, 113, 114, 116, 120, 122, 123, 124, 128, 129, 134, 135, 139, 141, 143, 145, 147, 148, 153, 155, 157, 161 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Inspired by Van der Waerden's Theorem, the positive integers are partitioned into two disjoint sequences, A and B, so that they obey the following rules:

Rule 1: For a given n, let A(n) and B(n) be the subsets of A and B with terms less than or equal to n. Any maximal arithmetic subsequence of A(n) must have at least as many terms as any maximal arithmetic subsequence of B(n).

Rule 2: Construct the sequences by starting at 1 and always favoring to add terms to B, unless it violates Rule 1. Add terms to A if they cannot be added to B.

The sequence listed here is the A sequence.

LINKS

Table of n, a(n) for n=1..63.

EXAMPLE

A gets 1, because B cannot yet have an AS of length 1.

B gets 2, because we favor adding to B and A already has an AS of length 1.

A gets 3, because B cannot yet form an AS of length 2.

B gets 4, because A now has an AS of length 2.

B gets 5, because 2,4,5 does not contain an AS of length 3.

A gets 6, because 2,4,5,6 would contain an AS of length 3.

MATHEMATICA

CheckMaxASFromEnd[A_, x_, m_] := Module[{i, n=Length[A], d, k}, If[ m>n+1, Return[False]; , ]; If[ And[ m<=n+1, n < 2], Return[True]; , ]; For[ i=n, i>0, i--, d = x-A[[i]]; bot = x-(m-1)*d; If[ bot <= 0, Break[]; , ]; For[ k=x-2*d, k>=x-(m-1)*d, k -= d, If[ MemberQ[A, k], If[ k == x-(m-1)*d, Return[True]; , ]; , Break[]; ]; ]; ]; False ];

ASRace[n_] := Module[{i, m=0, A={}, B={}}, For[i=1, i <= n, i++, If[ CheckMaxASFromEnd[B, i, m+1], If[ CheckMaxASFromEnd[A, i, m+1], m++, ]; A = Append[A, i]; , B = Append[B, i]; ]; ]; {A, B} ];

CROSSREFS

Sequence in context: A189637 A182338 A267415 * A310140 A231006 A231011

Adjacent sequences:  A140513 A140514 A140515 * A140517 A140518 A140519

KEYWORD

nonn

AUTHOR

Reed Kelly, Jul 01 2008

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 April 25 16:08 EDT 2019. Contains 322461 sequences. (Running on oeis4.)