

A276409


Number of reduced words of length n in the alphabet {U,U^(1),S,S^(1)} that are equal to unity if U^3 = S^2 = 1.


2



1, 0, 2, 2, 6, 24, 44, 136, 298, 914, 2462, 6464, 17740, 47840, 133618, 366162, 1011190, 2801144, 7775916, 21680712, 60443514, 168963010, 472975278, 1326349568, 3725180524, 10475012672, 29494512354, 83141905570, 234634612198, 662840458840, 1874315939756
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OFFSET

0,3


LINKS

Table of n, a(n) for n=0..30.
G. Alkauskas, The modular group and words in its two generators, arXiv:1512.02596 [math.NT], 20152017.
G. Alkauskas, The modular group and words in its two generators, Lithuanian Math. J. 57(1) (2017), 112.
Jason Bell and Marni Mishna, On the Complexity of the Cogrowth Sequence, arXiv:1805.08118 [math.CO], 2018.


CROSSREFS

Cf. A265434, A276408.
Sequence in context: A188962 A076741 A320603 * A093453 A301381 A342282
Adjacent sequences: A276406 A276407 A276408 * A276410 A276411 A276412


KEYWORD

nonn


AUTHOR

N. J. A. Sloane, Sep 14 2016


EXTENSIONS

Name changed, terms a(12) and beyond added using g.f. from Alkauskas by Andrey Zabolotskiy, Aug 03 2022


STATUS

approved



