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A172993
Maximal number of 4-tree rows in n-tree orchard problem in which the coordinates of trees may be complex numbers.
0
0, 0, 0, 1, 1, 1, 2, 2, 3, 5, 6, 9, 9, 11, 13, 15, 17, 18, 20, 23
OFFSET
1,7
EXAMPLE
a(12)=9: Such as 12 trees in 9 rows: example for 12 trees with 9 rows: ABCD,AEFG,AHIJ,BEHK,BFIL,CEJL,CGIK,DFJK,DGHL. Let t^2+t+1=0, coordinate in projective plane: A[0:1:0], B[1:0:0], C[1:1+t:0], D[1:t:0], E(0,0), F(0,1), G(0,-t), H(1,0), I(1,1), J(1,t+1), K(1+t,0), L(-t,1).
CROSSREFS
Cf. A006065.
Sequence in context: A326548 A326687 A352524 * A335755 A325338 A143438
KEYWORD
hard,more,nonn
AUTHOR
Zhao Hui Du, Feb 07 2010
EXTENSIONS
a(12) corrected by Zhao Hui Du, Oct 30 2019
STATUS
approved