OFFSET
1,2
COMMENTS
a(n) follows the Fibonacci recursion with an additional term (see Formula).
LINKS
Index entries for linear recurrences with constant coefficients, signature (1,1,0,0,1).
FORMULA
a(n) = a(n-1) + a(n-2) + a(n-5) with a(1) = 1, a(2) = 2, a(3) = 3, a(4) = 5, a(5) = 8.
G.f.: x*(1 + x)/(1 - x - x^2 - x^5). - Stefano Spezia, Jan 01 2021
EXAMPLE
a(5)=8: 00111, 01001, 01010, 01011, 01100, 01101, 01110, 01111. Note 01001 gets counted at n=5, 010011 at n=6, and 0100111 at n=7.
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Enrique Navarrete, Dec 31 2020
STATUS
approved