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 A327873 #8 Oct 03 2019 20:59:25
%S A327873 1,0,0,2,0,2,0,6,6,0,4,6,0,14,36,24,0,12,36,24,0,28,150,240,120,0,24,
%T A327873 144,240,120,0,62,540,1560,1800,720,0,54,534,1560,1800,720,0,126,1806,
%U A327873 8400,16800,15120,5040,0,112,1770,8376,16800,15120,5040
%N A327873 Irregular triangle read by rows: T(n,k) is the number of length n primitive (aperiodic) palindromes using exactly k different symbols, 1 <= k <= ceiling(n/2).
%H A327873 Andrew Howroyd, <a href="/A327873/b327873.txt">Table of n, a(n) for n = 1..2550</a>
%F A327873 T(n,k) = Sum_{j=1..k} (-1)^(k-j)*binomial(k,j)*A284823(n,j).
%F A327873 T(n,k) = Sum_{d|n} mu(n/d)*k!*Stirling2(ceiling(d/2), k).
%e A327873 Triangle begins:
%e A327873 1;
%e A327873 0;
%e A327873 0, 2;
%e A327873 0, 2;
%e A327873 0, 6, 6;
%e A327873 0, 4, 6;
%e A327873 0, 14, 36, 24;
%e A327873 0, 12, 36, 24;
%e A327873 0, 28, 150, 240, 120;
%e A327873 0, 24, 144, 240, 120;
%e A327873 0, 62, 540, 1560, 1800, 720;
%e A327873 0, 54, 534, 1560, 1800, 720;
%e A327873 0, 126, 1806, 8400, 16800, 15120, 5040;
%e A327873 0, 112, 1770, 8376, 16800, 15120, 5040;
%e A327873 ...
%o A327873 (PARI) T(n,k) = {sumdiv(n, d, moebius(n/d)*k!*stirling(ceil(d/2), k, 2))}
%Y A327873 Columns k=2..6 are A056463, A056464, A056465, A056466, A056467.
%Y A327873 Row sums are A327874.
%Y A327873 Cf. A284823, A327878.
%K A327873 nonn,tabf
%O A327873 1,4
%A A327873 _Andrew Howroyd_, Sep 28 2019