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A298802
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Growth series for group with presentation < S, T : S^4 = T^4 = (S*T)^4 = 1 >.
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12
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1, 4, 10, 24, 56, 128, 294, 676, 1552, 3564, 8186, 18800, 43176, 99160, 227734, 523020, 1201184, 2758676, 6335658, 14550664, 33417496, 76747632, 176260934, 404806196, 929690160, 2135154556, 4903660570, 11261895264, 25864409480, 59400985544, 136422101046, 313311125788, 719559813184
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OFFSET
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0,2
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LINKS
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FORMULA
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G.f.: (1 + x)^2*(1 + x^2) / (1 - 2*x - 2*x^3 + x^4).
a(n) = 2*a(n-1) + 2*a(n-3) - a(n-4) for n>4. - Colin Barker, Feb 04 2018
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MATHEMATICA
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LinearRecurrence[{2, 0, 2, -1}, {1, 4, 10, 24, 56}, 40] (* Harvey P. Dale, Jan 02 2020 *)
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PROG
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(Magma)
R<x> := RationalFunctionField(Integers());
PSR25 := PowerSeriesRing(Integers():Precision := 25);
FG<S, T> := FreeGroup(2);
TG := quo<FG | S^4, T^4, (S*T)^4 >;
f, A :=IsAutomaticGroup(TG);
gf := GrowthFunction(A);
R!gf;
Coefficients(PSR25!gf);
(PARI) Vec((1 + x)^2*(1 + x^2) / (1 - 2*x - 2*x^3 + x^4) + O(x^40)) \\ Colin Barker, Feb 04 2018
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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