OFFSET
1,2
LINKS
Colin Barker, Table of n, a(n) for n = 1..1000
Eric Weisstein's World of Mathematics, Clique Covering Number.
Eric Weisstein's World of Mathematics, Fiveleaper Graph.
Index entries for linear recurrences with constant coefficients, signature (2,0,-2,1).
FORMULA
a(n) = (3-(-1)^n + 2*(n-1)*(n+1))/4 for n > 6.
a(n) = 2*a(n-1) - 2*a(n-3) + a(n-4) for n >= 10.
G.f.: x*(-1 - 2*x - x^2 + 4*x^4 + 6*x^5 - 4*x^6 - 8*x^7 + 4*x^9)/((-1 +
x)^3*(1 + x)).
MATHEMATICA
Join[{1, 4, 9, 16, 21, 22}, Table[(3 + (-1)^n + 2 n (n + 2))/4, {n, 6, 20}]] (* Eric W. Weisstein, Apr 18 2019 *)
Join[{1, 4, 9, 16, 21, 22}, LinearRecurrence[{2, 0, -2, 1}, {25, 32, 41, 50}, 20]] (* Eric W. Weisstein, Apr 18 2019 *)
CoefficientList[Series[(-1 - 2 x - x^2 + 4 x^4 + 6 x^5 - 4 x^6 - 8 x^7 + 4 x^9)/((-1 + x)^3 (1 + x)), {x, 0, 20}], x] (* Eric W. Weisstein, Apr 18 2019 *)
PROG
(PARI) Vec(x*(1 + 2*x + x^2 - 4*x^4 - 6*x^5 + 4*x^6 + 8*x^7 - 4*x^9) / ((1 - x)^3*(1 + x)) + O(x^40)) \\ Colin Barker, Jul 26 2019
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Eric W. Weisstein, Mar 26 2018
EXTENSIONS
Extended by Eric W. Weisstein, Apr 18 2019
Extended by Colin Barker, Jul 26 2019
STATUS
approved