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A290699 a(n) = 2^n - n + n^2. 2
0, 2, 6, 14, 28, 52, 94, 170, 312, 584, 1114, 2158, 4228, 8348, 16566, 32978, 65776, 131344, 262450, 524630, 1048956, 2097572, 4194766, 8389114, 16777768, 33555032, 67109514, 134218430, 268436212, 536871724, 1073742694, 2147484578, 4294968288, 8589935648, 17179870306 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
COMMENTS
Number of minimal edge covers in the n-book graph.
LINKS
Eric Weisstein's World of Mathematics, Book Graph
Eric Weisstein's World of Mathematics, Minimal Edge Cover
FORMULA
a(n) = 2*A132109(n-1).
a(n) = 5*a(n-1) - 9*a(n-2) + 7*a(n-3) - 2*a(n-4).
G.f.: -((2 x (-1 + 2 x - x^2 + x^3))/((-1 + x)^3 (-1 + 2 x))).
MATHEMATICA
Table[2^n - n + n^2, {n, 20}]
LinearRecurrence[{5, -9, 7, -2}, {2, 6, 14, 28}, 20]
CoefficientList[Series[-((2 (-1 + 2 x - x^2 + x^3))/((-1 + x)^3 (-1 + 2 x))), {x, 0, 20}], x]
CROSSREFS
Cf. A132109.
A077265 is a subsequence.
Sequence in context: A294867 A033547 A050531 * A027083 A249665 A337106
KEYWORD
nonn,easy
AUTHOR
Eric W. Weisstein, Aug 09 2017
EXTENSIONS
Added a(0)=0. - N. J. A. Sloane, May 25 2019
STATUS
approved

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Last modified April 21 10:46 EDT 2024. Contains 371852 sequences. (Running on oeis4.)