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Number of homeomorphically irreducible leaf colored trees with n leaves using exactly 2 colors.
4

%I #8 Jan 10 2021 02:13:39

%S 0,1,2,7,24,91,354,1491,6504,29711,139616,674696,3328798,16730955,

%T 85382210,441571216,2310003732,12206975528,65082858008,349756996762,

%U 1892980028014,10310987833049,56489307860860,311112321625754,1721692801914844,9569930999155801,53410232801675436

%N Number of homeomorphically irreducible leaf colored trees with n leaves using exactly 2 colors.

%H Andrew Howroyd, <a href="/A339785/b339785.txt">Table of n, a(n) for n = 1..500</a>

%F a(n) = A339782(n) - 2*A007827(n).

%o (PARI) my(N=25); (U(N,2)-2*U(N,1))[2..1+N] \\ See A339780 for U(n,k).

%Y Column k=2 of A339780.

%Y Cf. A007827, A339782.

%K nonn

%O 1,3

%A _Andrew Howroyd_, Dec 16 2020