A377840 Cogrowth sequence of the 16-element group C8 X C2 = .

1, 1, 1, 1, 2, 46, 496, 3004, 12872, 43912, 130816, 394384, 1470944, 6874336, 33550336, 151869376, 622116992, 2353246336, 8589869056, 31961192704, 125858012672, 521796316672, 2199022206976, 9122012806144, 36758056208384, 144536687773696, 562949936644096

Offset: 0

Author

Sean A. Irvine, Nov 09 2024

Keywords

• nonn
• easy

Comments

Gives the even terms, all the odd terms are 0.

Examples

			a(4)=2 corresponds to the words SSSSSSSS and TTTTTTTT.
		

Links

• Index entries for linear recurrences with constant coefficients, signature (8,-28,56,-68,112,112,64).

Crossrefs

Cf. A007582 (D8), A377627 (C6 X C2), A377714 (C4 X C2).

Formula

G.f.: (8*x^7+28*x^6+42*x^5-34*x^4+35*x^3-21*x^2+7*x-1) / ((4*x-1) * (4*x^2+1) * (4*x^4+8*x^3+8*x^2-4*x+1)).