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 A308208 #16 Jul 15 2019 22:48:14 %S A308208 0,1101,110,12,112,23,102,34,13,45,334,56,24,67,554,14,35,89,130,667, %T A308208 46,25,342,887,15,889,314,36,68,241,11022,1164,26,47,546,16,124,425, %U A308208 46730,58,37,657,13132,415,214,27,12850,251,17,1707,146,235,553,2073,114,38,59,897,526,647 %N A308208 Least number k such that the determinant of the symmetric Hankel matrix formed by its decimal digits is equal to n negated. %C A308208 Records: 0, 1101, 11022, 46730, 52324, 54160, 1125004, 1162232, 1205240, 1252514, 1341680, 1663828, 3357554, 3741424, 4561735, 5069138, 9436293, 104562436, 122775666, 160205152, 165525440, 224394816, etc. %H A308208 Robert G. Wilson v, <a href="/A308208/b308208.txt">Table of n, a(n) for n = 0..10000</a> %H A308208 Wikipedia, <a href="https://en.wikipedia.org/wiki/Hankel_matrix">Hankel matrix</a> %e A308208 | 1 1 0 | %e A308208 a(2) = 110 because det | 1 0 1 | = -2 %e A308208 | 0 1 1 | %e A308208 ; %e A308208 a(5) = 23 because det | 2 3 | %e A308208 | 3 2 | = -5; etc. %p A308208 with(numtheory): with(linalg): P:=proc(q) local c, d, i, k, n, t: print(0); %p A308208 for i from 1 to q do for n from 1 to q do c:=convert(n, base, 10): t:=[]: %p A308208 for k from 1 to nops(c) do t:=[op(t), 0]: od: d:=t: t:=[]: %p A308208 for k from 1 to nops(c) do t:=[op(t), d]: t[k, -k]:=1: od: %p A308208 if det(evalm(toeplitz(c) &* t))=-i then print(n); break: fi: %p A308208 od: od: end: P(10^8); %t A308208 f[n_] := Block[{k = 0}, While[id = IntegerDigits@ k; -Det[HankelMatrix[id, Reverse@ id]] != n, k++]; k]; Array[f, 60, 0] %Y A308208 Cf. A308110. %K A308208 nonn,base %O A308208 0,2 %A A308208 _Paolo P. Lava_ and _Robert G. Wilson v_, May 15 2019