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

Offset: 4

Author

Mike Zabrocki, Nov 05 2006

Keywords

• nonn
• easy

Examples

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

Links

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

Crossrefs

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

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