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 A056459 #22 Apr 25 2020 01:16:04
%S A056459 3,0,6,6,24,18,78,72,234,216,726,696,2184,2106,6528,6480,19680,19422,
%T A056459 59046,58800,177060,176418,531438,530640,1594296,1592136,4782726,
%U A056459 4780776,14348904,14342112,43046718,43040160,129139428,129120480,387420384,387400104,1162261464,1162202418,3486782208
%N A056459 Number of primitive (aperiodic) palindromes using a maximum of three different symbols.
%D A056459 M. R. Nester (1999). Mathematical investigations of some plant interaction designs. PhD Thesis. University of Queensland, Brisbane, Australia. [See A056391 for pdf file of Chap. 2]
%F A056459 a(n) = Sum_{d | n} mu(d)*A056449(n/d).
%o A056459 (PARI) a(n) = sumdiv(n, d, moebius(d)*3^((1 + n/d)\2));
%o A056459 for(n=1, 40, print1(a(n), ",")); \\ _Petros Hadjicostas_, Apr 24 2020
%Y A056459 Cf. A056449.
%Y A056459 Column 3 of A284823.
%K A056459 nonn
%O A056459 1,1
%A A056459 _Marks R. Nester_
%E A056459 More terms from _Petros Hadjicostas_, Apr 24 2020