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 A322639 #22 Jan 30 2023 02:26:35 %S A322639 16,96,192,896,960,4608,6720 %N A322639 Number of solutions to |dft(a)^2 + dft(b)^2 + dft(c)^2 + dft(d)^2| = 4n, where a,b,c,d are +1,-1 sequences of length n and dft(x) denotes the discrete Fourier transform of x. %C A322639 Each solution (a,b,c,d) corresponds to a Hadamard matrix of quaternion type H = [[A, B, C, D], [-B, A, -D, C], [-C, D, A, -B], [-D, -C, B, A]], where A, B, C and D are circulant matrices formed by a, b, c and d, respectively. %C A322639 16 is a divisor of a(n), for all n. If (a,b,c,d) is a solution, then each of the 16 tuples ((+-)a, (+-)b, (+-)c, (+-)d) is also a solution. %C A322639 a(n) >= A321338(n). Every solution (a,b,c,d) that is counted by A321338(n) is also counted by a(n). %H A322639 Jeffery Kline, <a href="/A322639/a322639.txt">A complete list of solutions (a,b,c,d)</a>, for 1<=n<=7. %H A322639 Jeffery Kline, <a href="/A322639/a322639_1.txt">List of tuples (a,b,c,d) to demonstrate that a(n)>0</a>, for 1<=n<=22 and n=24. %Y A322639 Cf. A007299, A020985, A185064, A258218, A319594, A321338, A321851, A322617. %K A322639 nonn,more %O A322639 1,1 %A A322639 _Jeffery Kline_, Dec 21 2018