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A025569 T(2n-1,n), where T is the array defined in A025564. 0
1, 4, 22, 120, 665, 3732, 21153, 120835, 694590, 4013088, 23284424, 135580865, 791862354, 4637009300, 27215510265, 160053426720, 942939231825, 5564024727096, 32878367902380, 194530139772844, 1152303896900338, 6832908809693304, 40556775927067299, 240938382783554100 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..24.

PROG

(PARI) T(n, k) = if( k<0 || k>2*n, 0, if(n==0, 1, polcoeff( (1 + x + x^2)^n, k)+ polcoeff( (1 + x + x^2)^(n-1), k-1)));

a(n) = T(2*n, n+1); \\ Michel Marcus, Sep 08 2019

CROSSREFS

Cf. A025564.

Sequence in context: A155596 A244900 A261193 * A098834 A065983 A236576

Adjacent sequences:  A025566 A025567 A025568 * A025570 A025571 A025572

KEYWORD

nonn

AUTHOR

Clark Kimberling

EXTENSIONS

a(19) corrected and more terms from Sean A. Irvine, Sep 07 2019

STATUS

approved

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Last modified January 29 16:58 EST 2020. Contains 331347 sequences. (Running on oeis4.)