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%I #6 Feb 17 2018 10:56:13
%S 0,-1,4,-7,10,68,-578,3825,-14508,38367,-46170,37125,740520,7341147,
%T -211529660,2662060613,-31141230062,234276517760,-1130151516242,
%U 4893200552669,-6576135166508,7495109866067,233921918627644,6741771472435181,-80428962094730600
%N Determinant of the n X n matrix whose element (i,j) equals t(|i-j|) where t(n) is the number of divisors of n and t(0) = 0.
%H Iain Fox, <a href="/A071084/b071084.txt">Table of n, a(n) for n = 1..300</a>
%t f[n_] := Det[ Table[ If[i == j, 0, DivisorSigma[0, Abs[i - j]]], {i, 1, n}, {j, 1, n}]]; Table[Abs[f[n]], {n, 1, 21}]
%o (PARI) a(n) = matdet(matrix(n, n, i, j, if(i == j, 0, numdiv(abs(i-j))))) \\ _Iain Fox_, Feb 15 2018
%K sign
%O 1,3
%A _Robert G. Wilson v_, May 26 2002
%E a(22)-a(25) from _Iain Fox_, Feb 15 2018
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