OFFSET
1,1
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..1000
Eric Weisstein's World of Mathematics, Ladder Graph.
Index entries for linear recurrences with constant coefficients, signature (1,2).
FORMULA
a(n) = a(n-1) + 2*a(n-2) for n > 4.
G.f.: x*(3 + 5*x + 3*x^2 - x^3)/((1 + x)*(1 - 2*x)).
MATHEMATICA
LinearRecurrence[{1, 2}, {3, 8, 17, 32}, 50] (* Paolo Xausa, Oct 03 2024 *)
PROG
(PARI) Vec((3 + 5*x + 3*x^2 - x^3)/((1 + x)*(1 - 2*x)) + O(x^20))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Andrew Howroyd, Feb 23 2023
STATUS
approved