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A090822 Gijswijt's sequence: a(1) = 1; for n>1, a(n) = largest integer k such that the word a(1)a(2)...a(n-1) is of the form xy^k for words x and y (where y has positive length), i.e. the maximal number of repeating blocks at the end of the sequence so far. 74
1, 1, 2, 1, 1, 2, 2, 2, 3, 1, 1, 2, 1, 1, 2, 2, 2, 3, 2, 1, 1, 2, 1, 1, 2, 2, 2, 3, 1, 1, 2, 1, 1, 2, 2, 2, 3, 2, 2, 2, 3, 2, 2, 2, 3, 3, 2, 1, 1, 2, 1, 1, 2, 2, 2, 3, 1, 1, 2, 1, 1, 2, 2, 2, 3, 2, 1, 1, 2, 1, 1, 2, 2, 2, 3, 1, 1, 2, 1, 1, 2, 2, 2, 3, 2, 2, 2, 3, 2, 2, 2, 3, 3, 2, 2, 2, 3, 2, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Here xy^k means the concatenation of the words x and k copies of y.

The name "Gijswijt's sequence" is due to N. J. A. Sloane, not the author!

Fix n and suppose a(n) = k. Let len_y(n) = length of shortest y for this k and let len_x = n-1 - k*len_y(n) = corresponding length of x. A091407 and A091408 give len_y and len_x. For the subsequence when len_x = 0 see A091410 and A091411.

The first 4 occurs at a(220) (see A091409).

The first 5 appears around term 10^(10^23).

We believe that for all N >= 6, he first time N appears is at about position 2^(2^(3^(4^(5^...^(N-1))))). - N. J. A. Sloane and Allan Wilks, Mar 14 2004

Mar 04 2004: Allan Wilks observes that in the first 100000 terms the fraction of [1's, 2's, 3's, 4's] seems to converge, to about [.287, .530, .179, .005] respectively.

When k=12 is reached, say, it is treated as the number 12, not as 1,2. This is not a base-dependent sequence.

Does this sequence have a finite average? Does anyone know the exact value? - Franklin T. Adams-Watters, Jan 24 2008. Reply from Maximilian F. Hasler: Given the cited observation "...the fraction of [1's, 2's, 3's, 4's] seems to converge, to about [.287, .530, .179, .005]..." that average should be the dot product of these vectors, i.e. about 1.904.

REFERENCES

N. J. A. Sloane, Seven Staggering Sequences, in Homage to a Pied Puzzler, E. Pegg Jr., A. H. Schoen and T. Rodgers (editors), A. K. Peters, Wellesley, MA, 2009, pp. 93-110.

LINKS

N. J. A. Sloane, Table of n, a(n) for n = 1..24000

Andreas Abel and Andres Loeh, Haskell program for A090822

F. J. van de Bult, D. C. Gijswijt, J. P. Linderman, N. J. A. Sloane and _Allan Wilks_, A Slow-Growing Sequence Defined by an Unusual Recurrence, J. Integer Sequences, Vol. 10 (2007), #07.1.2.

F. J. van de Bult, D. C. Gijswijt, J. P. Linderman, N. J. A. Sloane and _Allan Wilks_, A Slow-Growing Sequence Defined by an Unusual Recurrence [pdf, ps].

B. Chaffin, J. P. Linderman, N. J. A. Sloane and _Allan Wilks_, On Curling Numbers of Integer Sequences, arXiv:1212.6102, Dec 25 2012.

B. Chaffin, J. P. Linderman, N. J. A. Sloane and _Allan Wilks_, On Curling Numbers of Integer Sequences, Journal of Integer Sequences, Vol. 16 (2013), Article 13.4.3.

Benjamin Chaffin and N. J. A. Sloane, The Curling Number Conjecture, preprint.

N. J. A. Sloane, The Curling Number Conjecture (Vugraph from a talk about the OEIS)

N. J. A. Sloane, Seven Staggering Sequences.

Index entries for sequences related to Gijswijt's sequence

Index entries for sequences related to curling numbers

MATHEMATICA

ClearAll[a]; reversed = {a[2]=1, a[1]=1}; blocs[len_] := Module[{bloc1, par, pos}, bloc1 = Take[reversed, len]; par = Partition[ reversed, len]; pos = Position[par, bloc_ /; bloc != bloc1, 1, 1]; If[pos == {}, Length[par], pos[[1, 1]] - 1]]; a[n_] := a[n] = Module[{an}, an = Table[{blocs[len], len}, {len, 1, Quotient[n-1, 2]}] // Sort // Last // First; PrependTo[ reversed, an]; an]; A090822 = Table[a[n], {n, 1, 99}] (* Jean-Fran├žois Alcover, Aug 13 2012 *)

PROG

(Haskell)  see link.

CROSSREFS

Cf. A091407, A091408, A091409 (records), A091410, A091411, A091579, A091586, A091970, A093955-A093958.

A091412 gives lengths of runs. A091413 gives partial sums.

Cf. also A094004, A160766, A217206, A217207.

Generalizations: A094781, A091975, A091976, A092331-A092335.

Sequence in context: A053633 A216460 A156755 * A091975 A091976 A151902

Adjacent sequences:  A090819 A090820 A090821 * A090823 A090824 A090825

KEYWORD

nonn,nice

AUTHOR

Dion Gijswijt (gijswijt(AT)science.uva.nl), Feb 27 2004

STATUS

approved

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Last modified April 21 08:49 EDT 2014. Contains 240824 sequences.