

A219218


G.f. satisfies: A(x) = Sum_{n>=0} [A(x)^(2*n) (mod 3)]*x^n, where A(x)^(2*n) (mod 3) reduces all coefficients modulo 3 to {0,1,2}.


1



1, 1, 3, 3, 1, 6, 9, 3, 3, 9, 3, 6, 3, 1, 15, 18, 6, 6, 27, 9, 12, 9, 3, 9, 9, 3, 3, 27, 9, 18, 9, 3, 18, 18, 6, 6, 9, 3, 6, 3, 1, 42, 45, 15, 15, 54, 18, 24, 18, 6, 18, 18, 6, 6, 81, 27, 36, 27, 9, 36, 36, 12, 12, 27, 9, 12, 9, 3, 27, 27, 9, 9, 27, 9, 12, 9, 3, 9, 9, 3, 3, 81, 27, 54
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OFFSET

0,3


LINKS

Paul D. Hanna, Table of n, a(n) for n = 0..500


FORMULA

a(n) == A001764(n) (mod 3), where A001764(n) = binomial(3*n,n)/(2*n+1).
G.f.: A(x) == G(x) (mod 3), where G(x) = 1 +x*G(x)^3 is the g.f. of A001764.
Define trisections by: A(x) = A0(x^3) + x*A1(x^3) + x^2*A2(x^3), then
A0(x) = 3*A(x)  2,
A1(x) = A(x),
A2(x^3) = (2+A(x)  (3+x)*A(x^3))/x^2.


PROG

(PARI) {A=1; for(i=1, 122, A=Ser(sum(n=0, #A1, Vec(1+x^n*A^(2*n) +x*O(x^#A))%3))#A); Vec(A+O(x^122))}


CROSSREFS

Cf. A080100.
Sequence in context: A082009 A110640 A143389 * A208524 A094040 A039798
Adjacent sequences: A219215 A219216 A219217 * A219219 A219220 A219221


KEYWORD

nonn


AUTHOR

Paul D. Hanna, Nov 14 2012


STATUS

approved



