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 A219357 #14 Feb 16 2025 08:33:18
%S A219357 17298,1352,28,28,320,81,133,104,247,126,1273,252,793,473,520,980,832,
%T A219357 513,468,5792,684,1738,2511,684,1520,14711,7588,938,3857,2275,4680,
%U A219357 13392,5184,1648,10535,1820,9143,8473,3843,21880,11609,3843
%N A219357 a(n) = smallest number greater than n, equal to the determinant of the circulant matrix formed by its base-n digits.
%C A219357 Trivially all one-digit matrices are solutions, which is why 'greater than n' is specified. Two-digit matrices can never be a solution, so entries are actually greater than n^2. Most terms are three-digit solutions (less than n^3). Known exceptions are 15 digits (base 2), 7 digits (base 3), and 4 digits (bases 6, 798, 1182).
%C A219357 Up to base 1200, coincident terms are 28, 684, 3843, 8190, 47664, 80199, 351819, 323505, 5879259, 601524, 17159660, 20777715, respectively for base pairs (4,5), (22,25), (40,43), (81,86), (94,97), (112,115), (184,187), (276,386), (472,475), (738,749), (1061,1066), (1131,1136).
%H A219357 Hans Havermann, <a href="/A219357/b219357.txt">Table of n, a(n) for n = 2..1200</a>
%H A219357 Hans Havermann, <a href="http://chesswanks.com/seq/a219357.png">log plot to base 1200</a>
%H A219357 Eric W. Weisstein, <a href="https://mathworld.wolfram.com/CirculantMatrix.html">MathWorld: Circulant Matrix</a>
%e A219357 In A219325 (base 2), the smallest number greater than 2 is 17298.
%e A219357 In A219324 (base 10), the smallest number greater than 10 is 247.
%t A219357 dcm[n_,b_] := (l = IntegerDigits[n,b]; Det[NestList[RotateRight, l, Length[l]-1]]); Table[i=b; While[dcm[i,b] != i, i++]; i, {b, 2, 43}]
%Y A219357 Cf. A219324 (base 10), A219325 (base 2).
%K A219357 nonn,base
%O A219357 2,1
%A A219357 _Hans Havermann_, Nov 18 2012