A371785 - OEIS

%I #7 Apr 06 2024 10:03:46

%S 1,3,14,76,441,2652,16303,101727,641630,4080154,26112384,167978615,

%T 1085182436,7035477777,45750406205,298279844724,1949096816505,

%U 12761551428024,83701819019155,549850618355886,3617119500327536,23824816811652905,157106267803712709

%N a(n) = Sum_{k=0..floor(n/2)} (-1)^k * binomial(3*n-k,n-2*k).

%F a(n) = [x^n] 1/((1-x+x^2) * (1-x)^(2*n)).

%o (PARI) a(n) = sum(k=0, n\2, (-1)^k*binomial(3*n-k, n-2*k));

%Y Cf. A024718, A371786, A371787.

%Y Cf. A371742.

%K nonn

%O 0,2

%A _Seiichi Manyama_, Apr 06 2024