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 A134978 #7 Apr 25 2024 09:31:41
%S A134978 0,1,6,15,28,53,74,111,152,209,246,339,384,473,582,695,756,917,986,
%T A134978 1175,1340,1493,1578,1855,2008,2193,2398,2683,2792,3185,3302,3603,
%U A134978 3880,4129,4446,4943,5084,5365,5698,6231,6388,6973,7138,7615,8172,8517,8698,9431
%N A134978 Number of 2 X 2 singular integer matrices with entries from {2,...,n}.
%H A134978 Charles R Greathouse IV, <a href="/A134978/b134978.txt">Table of n, a(n) for n = 1..500</a>
%F A134978 a(n) << n^(2+e) for all e > 0. - _Charles R Greathouse IV_, Jun 17 2013
%t A134978 a[n_] := Sum[Sum[Sum[Boole[d <= n && d > 1 && b*c/d <= n && b*c > d], {d, Divisors[b*c]}], {c, 2, n}], {b, 2, n}];
%t A134978 Table[a[n], {n, 1, 100}] (* _Jean-François Alcover_, Apr 25 2024, after _Charles R Greathouse IV_ *)
%o A134978 (PARI) a(n)=sum(b=2,n,sum(c=2,n,sumdiv(b*c,a, a<=n && a>1 && b*c/a<=n && b*c>a))) \\ _Charles R Greathouse IV_, Jun 17 2013
%Y A134978 Cf. A134506.
%K A134978 nice,nonn
%O A134978 1,3
%A A134978 Graziano Aglietti (mg5055(AT)mclink.it), Feb 04 2008