A290651 a(n) = 5 - 2^(n - 1) + 3^(n - 1) + n - 2.

4, 6, 11, 26, 73, 220, 675, 2070, 6317, 19184, 58039, 175114, 527361, 1586148, 4766603, 14316158, 42981205, 129009112, 387158367, 1161737202, 3485735849, 10458256076, 31376865331, 94134790246, 282412759293, 847255055040, 2541798719495, 7625463267290

Offset

1,1

Comments

For n > 2, number of irredundant sets in the (n-2)-book graph.

Links

Table of n, a(n) for n=1..28.

Eric Weisstein's World of Mathematics, Book Graph

Eric Weisstein's World of Mathematics, Irredundant Set

Index entries for linear recurrences with constant coefficients, signature (7, -17, 17, -6).

Formula

a(n) = 7*a(n-1) - 17*(n-2) + 17*a(n-3) - 6*a(n-4).

G.f.: (x (4 - 22 x + 37 x^2 - 17 x^3))/((-1 + x)^2 (1 - 5 x + 6 x^2)).

Mathematica

Table[5 - 2^(n - 1) + 3^(n - 1) + n - 2, {n, 20}]
LinearRecurrence[{7, -17, 17, -6}, {4, 6, 11, 26}, 20]
CoefficientList[Series[(4 - 22 x + 37 x^2 - 17 x^3)/((-1 + x)^2 (1 - 5 x + 6 x^2)), {x, 0, 20}], x]

Crossrefs

Sequence in context: A336343 A330459 A285994 * A358913 A066155 A105308

Adjacent sequences: A290648 A290649 A290650 * A290652 A290653 A290654

Keyword

nonn,easy

Author

Eric W. Weisstein, Aug 08 2017

Status

approved