A124721 - OEIS

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A124721

Number of ternary Lyndon words with exactly three 1's.

2, 8, 26, 80, 224, 596, 1536, 3840, 9384, 22528, 53248, 124240, 286720, 655360, 1485472, 3342336, 7471104, 16602432, 36700160, 80740352, 176859776, 385875968, 838860800, 1817531648, 3925868544, 8455716864, 18164132352, 38923141120

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OFFSET

4,1

LINKS

Table of n, a(n) for n=4..31.

Index entries for linear recurrences with constant coefficients, signature (6,-12,10,-12,24,-16).

FORMULA

G.f.: 2*x^4*(x - 1)^2/(1-2*x^3)/(1-2*x)^3 = (x^3/(1-2*x)^3-x^3/(1-2*x^3))/3

EXAMPLE

a(5) = 8 because 11122, 11212, 11123, 11132, 11213, 11312, 11133, 11313 are all ternary Lyndon words of length 5 with three 1's

CROSSREFS

Cf. A051168, A027376, A124720, A124722, A124723.

Sequence in context: A097040 A302237 A224289 * A279735 A103453 A024023

Adjacent sequences: A124718 A124719 A124720 * A124722 A124723 A124724

KEYWORD

nonn,easy

AUTHOR

Mike Zabrocki, Nov 05 2006

STATUS

approved