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 A362074 #11 Apr 09 2023 14:43:23
%S A362074 1,1,1,3,5,6,7,7,7,7,7,9,11,11,13,14,15,16,18,18,18,19,19,21,23,24,25,
%T A362074 26,27,27,28,29,30,31,32,33,34,35,36,36,37,38,39,40,41,42,43,44,45,45,
%U A362074 46,47,48,49,50,51,52,53,54,54,55,56,57,58,59,60,61,62,63
%N A362074 a(n) is the rank of the n X n symmetric matrix M(n) whose generic element M[i,j] = digsum(i*j).
%C A362074 The matrix M(n) is nonsingular (a(n) = n) only for n = 1, 5, 6 and 7 with determinant equal respectively to 1, 6561, 59049 and -531441.
%t A362074 M[i_, j_]:=Total[IntegerDigits[i*j]]; Table[MatrixRank[Table[M[i, j], {i, n}, {j, n}]], {n, 69}]
%o A362074 (PARI) a(n)=matrank(matrix(n,n,i,j,sumdigits(i*j))) \\ _Andrew Howroyd_, Apr 08 2023
%Y A362074 Cf. A003991, A007953, A353933, A362072, A362073 (permanent).
%K A362074 nonn,base
%O A362074 1,4
%A A362074 _Stefano Spezia_, Apr 08 2023