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 A339786 #8 Jan 10 2021 02:13:42 %S A339786 0,0,1,9,63,412,2673,17571,117365,798819,5530122,38908380,277750749, %T A339786 2009160864,14707923021,108835512411,813241695330,6130521151377, %U A339786 46584949832013,356571373433217,2747371943624943,21296479544449677,165994877608025730,1300408539157086640 %N A339786 Number of homeomorphically irreducible leaf colored trees with n leaves using exactly 3 colors. %H A339786 Andrew Howroyd, <a href="/A339786/b339786.txt">Table of n, a(n) for n = 1..500</a> %F A339786 a(n) = A339783(n) - 3*A339782(n) + 3*A007827(n). %o A339786 (PARI) my(N=25); (U(N,3) - 3*U(N,2) + 3*U(N,1))[2..1+N] \\ See A339780 for U(n, k). %Y A339786 Column k=3 of A339780. %Y A339786 Cf. A007827, A339782, A339783, A339785. %K A339786 nonn %O A339786 1,4 %A A339786 _Andrew Howroyd_, Dec 18 2020