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A071969 a(n) = Sum_{k=0..floor(n/3)} (binomial(n+1, k)*binomial(2*n-3*k, n-3*k)/(n+1)). 7
1, 1, 2, 6, 19, 63, 219, 787, 2897, 10869, 41414, 159822, 623391, 2453727, 9733866, 38877318, 156206233, 630947421, 2560537092, 10435207116, 42689715279, 175243923783, 721649457417, 2980276087005, 12340456995177, 51222441676513, 213090270498764, 888321276659112 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Diagonal of A071946. - Emeric Deutsch, Dec 15 2004

Last (largest) number of each row of A071946. - David Scambler, May 15 2012

LINKS

Table of n, a(n) for n=0..27.

D. Merlini et al., Underdiagonal lattice paths with unrestricted steps, Discrete Appl. Math., 91 (1999), 197-213 (d_n page 209).

FORMULA

G.f. (offset 1) is series reversion of (x-x^2)/(1+x^3).

MAPLE

A071969 := n->add( binomial(n+1, k)*binomial(2*n-3*k, n-3*k)/(n+1), k=0..floor(n/3));

Order:=30: g:=solve(series((H-H^2)/(1+H^3), H)=z, H): seq(coeff(g, z^n), n=1..28); # Emeric Deutsch, Dec 15 2004

PROG

(PARI) a(n)=if(n<0, 0, polcoeff(serreverse((x-x^2)/(1+x^3)+x^2*O(x^n)), n+1))

CROSSREFS

Cf. A071946 is the triangle and A119254 has the row sums.

Sequence in context: A001168 A193111 A119255 * A063030 A206463 A148467

Adjacent sequences:  A071966 A071967 A071968 * A071970 A071971 A071972

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Jun 17 2002

STATUS

approved

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Last modified October 17 01:03 EDT 2019. Contains 328103 sequences. (Running on oeis4.)