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A307395
Expansion of 1/((1 - x) * ((1 - x)^3 + x^3)).
2
1, 4, 10, 19, 28, 28, 1, -80, -242, -485, -728, -728, 1, 2188, 6562, 13123, 19684, 19684, 1, -59048, -177146, -354293, -531440, -531440, 1, 1594324, 4782970, 9565939, 14348908, 14348908, 1, -43046720, -129140162, -258280325, -387420488, -387420488, 1, 1162261468
OFFSET
0,2
FORMULA
a(n) = Sum_{k=0..floor(n/3)} (-1)^k*binomial(n+3,3*k+3).
a(n) = 4*a(n-1) - 6*a(n-2) + 3*a(n-3) for n > 2.
a(6*n) = 1.
a(n) = 1 - A057681(n+3). - Yomna Bakr and Greg Dresden, Apr 22 2024
MATHEMATICA
LinearRecurrence[{4, -6, 3}, {1, 4, 10}, 38] (* Amiram Eldar, May 13 2021 *)
PROG
(PARI) {a(n) = sum(k=0, n\3, (-1)^k*binomial(n+3, 3*k+3))}
(PARI) N=66; x='x+O('x^N); Vec(1/((1-x)*((1-x)^3+x^3)))
CROSSREFS
Column 5 of A307394.
Partial sums of A057083.
Sequence in context: A033263 A145731 A162958 * A029714 A348239 A062198
KEYWORD
sign,easy
AUTHOR
Seiichi Manyama, Apr 07 2019
STATUS
approved