

A160393


Square root of A003462, rounded up.


1



1, 2, 4, 7, 11, 20, 34, 58, 100, 172, 298, 516, 893, 1547, 2679, 4640, 8036, 13918, 24107, 41754, 72320, 125262, 216960, 375786, 650880, 1127357, 1952639, 3382070, 5857917, 10146210, 17573751, 30438629, 52721251, 91315885, 158163753, 273947655, 474491257, 821842965
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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^n1)/2)).


PROG

(PARI) a(n) = ceil(sqrt((3^n1)/2)); \\ Michel Marcus, Oct 20 2016


CROSSREFS

Cf. A090246, A003462.
Sequence in context: A151992 A242362 A024501 * A018173 A288380 A146156
Adjacent sequences: A160390 A160391 A160392 * A160394 A160395 A160396


KEYWORD

easy,nonn


AUTHOR

Jack W Grahl, May 12 2009


STATUS

approved



