This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A260908 #16 Aug 16 2015 03:31:07
%S A260908 1,-2,3,-12,15,45,-105,420,-1890,-4725,10395,31185,-135135,-315315,
%T A260908 -4729725,4729725,-80405325,-723647925,1527701175,7638505875,
%U A260908 53469541125,117632990475,-245959889175,-737879667525,18446991688125,79936963981875,-2158298027510625
%N A260908 Numerator of 1/det(M) where M is the n X n matrix with M[i,j] = 1/gcd(i,j).
%C A260908 Negative terms for n: 2, 4, 7, 9, 10, 13, 14, 15, 17, 18, 23, 24, 27, 28, 30, ..., .
%t A260908 f[n_] := 1/Det[ Table[ 1/GCD[i, j], {i, n}, {j, n}]]; Numerator@ Array[f, 27]
%o A260908 (PARI) vector(40, n, numerator(1/matdet(matrix(n, n, i, j, 1/gcd(i, j))))) \\ _Michel Marcus_, Aug 06 2015
%Y A260908 Cf. A060841, A260909.
%K A260908 sign
%O A260908 1,2
%A A260908 _Robert G. Wilson v_, Aug 04 2015