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 A069580 #11 Jul 12 2025 08:34:43
%S A069580 2,160,176128,2973761536,790377061679104,3337070496489549070336,
%T A069580 224673304169436873829314985984,
%U A069580 241628003280411784073600553618302304256,4154447778684876644944282114016459737751307157504,1142419984262996237357582885893433282120743128964441021874176
%N A069580 Number of noninvertible n X n matrices mod 4 (i.e., over the ring Z_4).
%F A069580 a(n) = 4^(n^2) - A065128(n).
%F A069580 a(n) ~ c * 4^(n^2), where c = 1 - A048651. - _Amiram Eldar_, Jul 12 2025
%t A069580 a[n_] := 4^(n^2) * (1 - Product[1 - 1/2^k, {k, 1, n}]); Array[a, 10] (* _Amiram Eldar_, Jul 12 2025 *)
%o A069580 (PARI) a(n) = 4^(n^2) * (1 - prod(k = 1, n, 1-1/2^k)); \\ _Amiram Eldar_, Jul 12 2025
%Y A069580 Cf. A011787, A048651, A065128.
%K A069580 nonn
%O A069580 1,1
%A A069580 Sharon Sela (sharonsela(AT)hotmail.com), Apr 18 2002
%E A069580 More terms from _Max Alekseyev_, Jan 23 2012