OFFSET
3,1
LINKS
Robert Israel, Table of n, a(n) for n = 3..10000
M. Svanstrom, A lower bound for ternary constant weight codes, IEEE Trans. on Information Theory, Vol. 43, pp. 1630-1632, Sep. 1997.
Index entries for linear recurrences with constant coefficients, signature (2,-1,1,-2,1).
FORMULA
a(n) = ceiling(binomial(n, w) * 2^w / (2*n + 1)) with w=3.
Conjectures from Colin Barker, Aug 02 2019: (Start)
G.f.: x^3*(2 + 2*x^2 - x^3 + x^4) / ((1 - x)^3*(1 + x + x^2)).
a(n) = 2*a(n-1) - a(n-2) + a(n-3) - 2*a(n-4) + a(n-5) for n>7.
(End)
From Robert Israel, Jul 09 2020: (Start)
Conjectures confirmed.
a(n) = (2*n^2-7*n+8)/3 if n == 1 (mod 3), otherwise a(n) = (2*n^2-7*n+9)/3.
(End)
MAPLE
g:= n -> (2*n^2-7*n+`if`(n mod 3 = 1, 8, 9))/3:
map(g, [$3..100]); # Robert Israel, Jul 09 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Mattias Svanstrom (mattias(AT)isy.liu.se)
STATUS
approved