Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #4 May 18 2023 23:26:48
%S 4,44,46,48,50,51,52,68,69,77,81,86,87,93,99,100,108,110,118,126,130,
%T 141,161,162,165,168,174,175,184,185,192,201,202,205,209,214,215,217,
%U 218,225,226,230,234,235,244,247,249,250
%N Numbers k>3 such that the divisibility tournament on 2..k has an odd determinant.
%C Let n be a positive integer, n>3. Define a tournament on the vertex set {2,3,...n} by: for i< j, i is adjacent to j if i divides j, else, j is adjacent to i and let T(n) be its adjacency matrix. It appears that values of n for which det(T(n)) is odd are rather sparse.
%Y Positions of odd terms in A057980.
%K nonn,more
%O 1,1
%A Rebecca A. Winslow (raw5(AT)students.uwf.edu), Aug 21 2001
%E Offset correct, a(1) inserted, and a(22)-a(48) from _Sean A. Irvine_, May 18 2023