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A308589
Number of minimal edge covers in the (2n-1)-triangular snake graph.
0
0, 3, 7, 17, 44, 112, 285, 726, 1849, 4709, 11993, 30544, 77790, 198117, 504568, 1285043, 3272771, 8335153, 21228120, 54064164, 137691601, 350675486, 893106737, 2274580561, 5792943345, 14753573988, 37574671882, 95695861097, 243719968064, 620710469107, 1580836767375
OFFSET
1,2
LINKS
Eric Weisstein's World of Mathematics, Minimal Edge Cover
Eric Weisstein's World of Mathematics, Triangular Snake Graph
FORMULA
a(n) = 2*a(n-1) + a(n-2) + a(n-3).
G.f.: -x^2*(3 + x)/(-1 + 2*x + x^2 + x^3).
MATHEMATICA
Table[-RootSum[-1 - # - 2 #^2 + #^3 &, -43 #^n - 99 #^(n + 1) + 40 #^(n + 2) &]/87, {n, 20}]
LinearRecurrence[{2, 1, 1}, {0, 3, 7}, 20]
CoefficientList[Series[-x (3 + x)/(-1 + 2 x + x^2 + x^3), {x, 0, 20}], x]
CROSSREFS
Sequence in context: A123601 A115325 A294129 * A018025 A018026 A087953
KEYWORD
nonn
AUTHOR
Eric W. Weisstein, Jun 09 2019
STATUS
approved