A378254 Cogrowth sequence of the 20-element group C10 X C2 = .

1, 1, 1, 1, 1, 2, 67, 1002, 8009, 43759, 184758, 646878, 1971883, 5541966, 16231216, 60090032, 290305577, 1523150157, 7564006759, 34099637859, 139541849878, 526321168143, 1878476551128, 6603812572941, 24052434515891, 94278969044262, 396750746960712

Offset: 0

Author

Sean A. Irvine, Nov 20 2024

Keywords

• nonn
• easy

Comments

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

Crossrefs

Cf. A377840 (C8 X C2), A377627 (C6 X C2), A078789 (D10).

Formula

G.f.: (10*x^9+75*x^8+162*x^7-48*x^6+127*x^5-126*x^4+84*x^3-36*x^2+9*x-1) / ((4*x-1) * (25*x^4+10*x^2-5*x+1) * (x^4+4*x^3+6*x^2-x+1)).