OFFSET
1,2
LINKS
Eric Weisstein's World of Mathematics, Minimal Edge Cover
Eric Weisstein's World of Mathematics, Triangular Snake Graph
Index entries for linear recurrences with constant coefficients, signature (2, 1, 1).
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
KEYWORD
nonn
AUTHOR
Eric W. Weisstein, Jun 09 2019
STATUS
approved