A285492 a(n) is the least positive integer not already appearing such that no two distinct, unordered pairs of distinct points ((n, a(n)), (m, a(m))) and ((k, a(k)), (j, a(j))) have the same midpoint.

1, 2, 3, 5, 4, 8, 11, 6, 15, 12, 9, 7, 20, 25, 16, 30, 36, 10, 18, 47, 27, 38, 59, 13, 58, 73, 43, 81, 19, 26, 96, 14, 45, 109, 121, 72, 54, 44, 70, 17, 98, 137, 60, 156, 29, 113, 155, 92, 22, 145, 173, 63, 112, 46, 39, 136, 204, 24, 219, 174, 21, 237, 253, 80

Offset: 1

Author

Peter Kagey, Apr 19 2017

Keywords

• nonn
• look

Examples

			a(4) != 4 or else midpoint((4,4), (1,1)) = midpoint((2,2), (3,3)), thus
a(4) = 5.
a(6) != 6 or else midpoint((6,6), (3,3)) = midpoint((4,5), (5,4));
a(6) != 7 or else midpoint((6,7), (1,1)) = midpoint((3,3), (4,5)); thus
a(6) = 8.
		

Links

• Giovanni Resta, Table of n, a(n) for n = 1..3000 (first 650 terms from Peter Kagey)

Crossrefs

Cf. A285490.