A092275 Draw a line through every pair of points with coordinates (x, 1) and (x', 2) with x, x' in 1..n, and then count the number of intersection points above the line y = 2.

0, 2, 11, 29, 69, 125, 224, 361, 563, 809, 1164, 1597, 2188, 2871, 3714, 4701, 5956, 7359, 9099, 11067, 13365, 15879, 18884, 22201, 26056, 30219, 34951, 40117, 46073, 52441, 59716, 67599, 76320, 85569, 95790, 106701, 118902

Offset: 2

Author

N. J. A. Sloane, Feb 17 2004

Keywords

• nonn

Links

• Joseph O'Rourke, Art Gallery Theorems and Algorithms, Oxford Univ. Press, 1987. See section 8.6, p. 223.

Crossrefs

Cf. A331755, A347750.

Formula

a(n) = (A347750(n-1) - A331755(n)) / 2. - Andrey Zabolotskiy, Jan 17 2024

Extensions

New name and terms a(10) and beyond (using the formula) added by Andrey Zabolotskiy, Jan 18 2024