OFFSET
0,2
LINKS
Colin Barker, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (1,1,1).
FORMULA
a(n) = 8*A000073(n) for n >= 3.
From Colin Barker, Aug 09 2019: (Start)
G.f.: (1 + x + x^2 + x^3 + 2*x^4 + 4*x^5) / (1 - x - x^2 - x^3).
a(n) = a(n-1) + a(n-2) + a(n-3) for n>5.
(End)
EXAMPLE
For n = 6 there are 8 strings omitted, namely 000000, 001001, ..., 111111, so a(6) = 64-8 = 56.
PROG
(PARI) Vec((1 + x + x^2 + x^3 + 2*x^4 + 4*x^5) / (1 - x - x^2 - x^3) + O(x^40)) \\ Colin Barker, Aug 09 2019
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Nathaniel Johnston, Oct 11 2013
STATUS
approved