cp's OEIS Frontend

A285490 Lexicographically earliest sequence 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.

%I A285490 #19 Dec 12 2023 13:46:11
%S A285490 1,1,1,2,1,3,5,1,7,4,9,12,1,17,21,28,6,27,2,16,14,22,41,1,50,11,33,61,
%T A285490 9,4,73,58,88,97,40,2,26,19,95,82,45,15,1,96,54,66,125,143,57,138,10,
%U A285490 1,171,92,184,178,191,54,110,160,13,3,202,217,122,88,42
%N A285490 Lexicographically earliest sequence 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.
%H A285490 Giovanni Resta, <a href="/A285490/b285490.txt">Table of n, a(n) for n = 1..4000</a> (first 650 terms from Peter Kagey)
%e A285490 a(1) = 1;
%e A285490 a(2) = 1;
%e A285490 a(3) = 1;
%e A285490 a(4) != 1 or else midpoint((1, 1), (4, 1)) = midpoint((2, 1), (3, 1));
%e A285490 a(4) = 2;
%e A285490 a(5) = 1;
%e A285490 a(6) != 1 or else midpoint((1, 1), (6, 1)) = midpoint((2, 1), (5, 1));
%e A285490 a(6) != 2 or else midpoint((3, 1), (6, 2)) = midpoint((4, 2), (5, 1));
%e A285490 a(6) = 3.
%Y A285490 Cf. A285491 (pairs of not necessarily distinct points).
%K A285490 nonn,look
%O A285490 1,4
%A A285490 _Peter Kagey_, Apr 19 2017