OFFSET
0,2
COMMENTS
Number of black cells after n iterations of Haferman's carpet.
LINKS
Colin Barker, Table of n, a(n) for n = 0..1000
Eric Weisstein's World of Mathematics, Haferman Carpet
Index entries for linear recurrences with constant coefficients, signature (4,45).
FORMULA
From Colin Barker, Jun 08 2013: (Start)
a(n) = 4*a(n-1) + 45*a(n-2).
G.f.: -1 / ((5*x+1)*(9*x-1)).
(End)
PROG
(PARI) Vec(1 / ((1 + 5*x)*(1 - 9*x)) + O(x^40)) \\ Colin Barker, Feb 26 2020
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Eric W. Weisstein, Apr 09 2006
STATUS
approved