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A229644
Cogrowth function of the group Baumslag-Solitar(2,2).
10
1, 4, 28, 244, 2396, 25324, 281140, 3232352, 38151196, 459594316, 5628197948, 69859456440, 876985904276, 11115789165888, 142066687799680, 1828884017527504, 23694360858872604, 308714491495346028, 4042605442981407388, 53178663502737007352
OFFSET
0,2
COMMENTS
a(n) is the number of words of length 2n in the letters a,a^{-1},t,t^{-1} that equal the identity of the group BS(2,2)=<a,t | ta^2=a^2t>.
LINKS
EXAMPLE
For n=1 there are 4 words of length 2 equal to the identity: aa^{-1}, a^{-1}a, tt^{-1}, t^{-1}t.
CROSSREFS
The cogrowth sequences for BS(N,N) for N = 1..10 are A002894, A229644, A229645, A229646, A229647, A229648, A229649, A229650, A229651, A229652.
Sequence in context: A192625 A199561 A103211 * A354602 A228714 A371693
KEYWORD
nonn,walk
AUTHOR
Murray Elder, Sep 27 2013
STATUS
approved