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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 (list; graph; refs; listen; history; text; internal format)
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) = ceil(sqrt((3^n-1)/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

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Last modified December 17 02:29 EST 2018. Contains 318192 sequences. (Running on oeis4.)