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 A177066 #12 May 14 2019 22:02:35 %S A177066 1,2,8,48,288,2880,34560,276480,4423680,79626240,955514880, %T A177066 21021327360,420426547200,7567677849600,211894979788800, %U A177066 6356849393664000,127136987873280000,3051287708958720000,109846357522513920000 %N A177066 Determinant of the symmetric n X n matrix M defined by M(i,j) = gcd(2i-1,2j-1) for 1 <= i,j <= n. %C A177066 It appears, but has not been proved, that the ratios a(n+1)/a(n) give phi(2n+1) (A037225). %C A177066 See A001088, A059381, and A059382 for determinants of matrices M defined by M(i,j) = gcd(i,j), gcd(i^2,j^2), and gcd(i^3,j^3), respectively. %p A177066 A177066 := proc(n) M := Matrix(n) ; for i from 1 to n do for j from 1 to n do M[i,j] := igcd(2*i-1,2*j-1) ; end do: end do: LinearAlgebra[Determinant](M) ; end proc: # _R. J. Mathar_, Dec 10 2010 %Y A177066 Cf. A001088, A037225, A059381, A059382. %K A177066 nonn %O A177066 1,2 %A A177066 _John W. Layman_, Dec 09 2010