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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.

%I A285492 #15 Dec 12 2023 13:46:49
%S A285492 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,
%T A285492 43,81,19,26,96,14,45,109,121,72,54,44,70,17,98,137,60,156,29,113,155,
%U A285492 92,22,145,173,63,112,46,39,136,204,24,219,174,21,237,253,80
%N 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.
%H A285492 Giovanni Resta, <a href="/A285492/b285492.txt">Table of n, a(n) for n = 1..3000</a> (first 650 terms from Peter Kagey)
%e A285492 a(4) != 4 or else midpoint((4,4), (1,1)) = midpoint((2,2), (3,3)), thus
%e A285492 a(4) = 5.
%e A285492 a(6) != 6 or else midpoint((6,6), (3,3)) = midpoint((4,5), (5,4));
%e A285492 a(6) != 7 or else midpoint((6,7), (1,1)) = midpoint((3,3), (4,5)); thus
%e A285492 a(6) = 8.
%Y A285492 Cf. A285490.
%K A285492 nonn,look
%O A285492 1,2
%A A285492 _Peter Kagey_, Apr 19 2017