OFFSET
0,2
COMMENTS
In the half-Manhattan lattice, E-W streets run alternately E and W, but N-S streets are two way.
LINKS
Paolo Xausa, Table of n, a(n) for n = 0..10000
Sean A. Irvine, Illustration of a(0) to a(7)
Index entries for linear recurrences with constant coefficients, signature (2,-1).
FORMULA
G.f.: (1+x) * (1+2*x^2-x^3) / (1-x)^2.
a(n) = 4*n, n >= 3.
MATHEMATICA
LinearRecurrence[{2, -1}, {1, 3, 7, 12, 16}, 100] (* Paolo Xausa, Sep 01 2023 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Sean A. Irvine, Jul 31 2020
STATUS
approved