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 A317291 #40 Jan 25 2024 14:31:05 %S A317291 0,1001,1012,1023,1034,1045,1056,1067,1078,1089,1100,1122,1133,1144, %T A317291 1155,1166,1177,1188,1199,1210,1221,1232,1243,1254,1265,1276,1287, %U A317291 1298,1320,1331,1342,1353,1364,1375,1386,1397,1430,1441,1452,1463,1474,1485,1496 %N A317291 Numbers k not in A239019 such that A177894(k) = 0. %C A317291 Of course A177894(A239019(n)) = 0 because the corresponding circular matrices each contains at least two identical rows or columns. This sequence gives the other numbers. %C A317291 A four-digit number abcd is in this sequence if and only if a + c = b + d and (a != c or b != d). %H A317291 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CirculantMatrix.html">Circulant Matrix</a>. %H A317291 Wikipedia, <a href="https://en.wikipedia.org/wiki/Circulant_matrix">Circulant matrix</a>. %e A317291 2178 is a term because the value of the following determinant is 0, although the determinant itself contains no identical rows or columns: %e A317291 | 2 1 7 8 | %e A317291 | 1 7 8 2 | %e A317291 | 7 8 2 1 | %e A317291 | 8 2 1 7 | %o A317291 (PARI) for(n=0, 1500, if(!n ||(n&!A177894(n)&&!A239019(n)),print1(n, ", "))) \\ See A177894 and A239019 for their programs %Y A317291 Cf. A177894, A239019, A299792. %K A317291 nonn,base %O A317291 1,2 %A A317291 _Jianing Song_, Jan 21 2019