%I #9 Oct 19 2019 04:16:18

%S 2,20,1308,10199370,131487690152

%N Y-coordinate of the first n*n non-coprime block above the line x=y in the first quadrant.

%C a(n) is the minimum y that satisfies x <= y and the GCD of (x,y),(x+1,y), ..., (x+n-1,y), (x,y+1),(x+1,y+1), ..., (x+n-1,y+1), ..., (x,y+n-1),(x+1,y+n-1), ..., (x+n-1,y+n-1) are all larger than 1.

%D Stephen Wolfram, A New Kind of Science, Wolfram Media, 2002, p. 1093.

%H The first 4 terms are found in Stephen Wolfram <a href="http://www.wolframscience.com/nksonline/toc.html">A New Kind of Science</a>

%H The 5th term has been posted on <a href="http://bbs.emath.ac.cn/viewthread.php?tid=1948&amp;page=4&amp;fromuid=1394#pid24048">bbs.emath.ac.cn</a>

%e a(2)=20 because the GCDs of (14,20), (15,20), (14,21), (15,21) are all larger than 1, and there is no such array within x <= y < 20.

%K nonn,hard,more

%O 1,1

%A _Yi Yang_, Jul 20 2010