OFFSET
1,2
COMMENTS
This sequence gives a lower bound for A090246. A003462 is the number of points in P(Z/3Z)^n. If a subset of P(Z/3Z)^n contains m points with no 3 collinear, then there are at most 2*C(m,2) points which are collinear with 2 points of the subset. Therefore if m + 2*C(m,2) = m^2 < A003462(n) we can add at least one more point to the set.
LINKS
Chai Wah Wu, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = ceiling(sqrt((3^n-1)/2)).
PROG
(PARI) a(n) = sqrtint((3^n-3)/2)+1; \\ Michel Marcus, Oct 20 2016; corrected Jun 15 2022
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jack W Grahl, May 12 2009
STATUS
approved