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A138341
Expansion of (1-4x-x^3)/(1-x+x^2)^2.
2
1, -2, -7, -7, 2, 13, 13, -2, -19, -19, 2, 25, 25, -2, -31, -31, 2, 37, 37, -2, -43, -43, 2, 49, 49, -2, -55, -55, 2, 61, 61, -2, -67, -67, 2, 73, 73, -2, -79, -79, 2, 85, 85, -2, -91, -91, 2, 97, 97, -2, -103, -103, 2, 109, 109, -2, -115, -115, 2, 121, 121, -2
OFFSET
0,2
COMMENTS
Hankel transform of A079309.
FORMULA
a(n) = (2n+1)*cos(Pi*n/3) - (2n+5)*sin(Pi*n/3)/sqrt(3).
a(n) = 2*a(n-1) - 3*a(n-2) + 2*a(n-3) - a(n-4) for n > 3. - Jinyuan Wang, Apr 09 2020
MATHEMATICA
CoefficientList[Series[(1-4x-x^3)/(1-x+x^2)^2, {x, 0, 100}], x] (* or *) LinearRecurrence[{2, -3, 2, -1}, {1, -2, -7, -7}, 100] (* Harvey P. Dale, Sep 23 2021 *)
PROG
(PARI) Vec((1-4*x-x^3)/(1-x+x^2)^2 + O(x^62)) \\ Jinyuan Wang, Apr 09 2020
CROSSREFS
Sequence in context: A159790 A251809 A016639 * A374525 A374526 A153520
KEYWORD
sign,easy
AUTHOR
Paul Barry, Mar 15 2008
EXTENSIONS
More terms from Jinyuan Wang, Apr 09 2020
STATUS
approved