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, 1, 1, 1, 2, 2, 3, 5, 6, 9, 9, 11, 13, 15, 17, 18, 20, 23

Offset: 1

Author

Zhao Hui Du, Feb 07 2010

Keywords

• hard
• more
• nonn

Examples

			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).
		

Links

• Zhao Hui Du, Orchard planting problem with 4 trees per row

Crossrefs

Cf. A006065.

Extensions

a(12) corrected by Zhao Hui Du, Oct 30 2019