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A113047 a(n) = C(3n,n)/(2n+1) mod 3. 4

%I

%S 1,1,0,0,1,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,

%T 0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,

%U 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1

%N a(n) = C(3n,n)/(2n+1) mod 3.

%C Conjecture: a(n) differs from 0 only when n=(3^j-1)/2,j=0,1,...

%H Antti Karttunen, <a href="/A113047/b113047.txt">Table of n, a(n) for n = 0..29524</a>

%F G.f.: A(x) satisfies A(x)=1+x*A(x^3). - _Vladimir Kruchinin_, Mar 24 2015

%F a(n) = A001764(n) mod 3. - _Michel Marcus_, Mar 24 2015

%t Table[Mod[Binomial[3 n, n]/(2 n + 1), 3], {n, 0, 72}] (* _Michael De Vlieger_, Mar 24 2015 *)

%o (PARI) A113047(n) = ((binomial(3*n,n)/(n+n+1))%3); \\ _Antti Karttunen_, Aug 28 2017

%Y Cf. A001764, A003462, A010872, A039969.

%K easy,nonn

%O 0,1

%A _Paul Barry_, Oct 11 2005

%E More terms from _Antti Karttunen_, Aug 28 2017

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Last modified November 17 13:29 EST 2019. Contains 329230 sequences. (Running on oeis4.)