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A337350 a(n) is the number of lattice paths from (0,0) to (2n,2n) using only the steps (1,0) and (0,1) and which do not touch any other points of the form (2k,2k). 2
1, 6, 34, 300, 3146, 36244, 443156, 5646040, 74137050, 996217860, 13633173180, 189347631720, 2662142601924, 37815138677960, 541882155414376, 7823955368697776, 113712609033955834, 1662288563798703204, 24424940365489658540, 360537080085493670856 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

The terms of this sequence may be computed via a determinant; see Lemma 10.7.2 of the Krattenthaler reference for details.

LINKS

Table of n, a(n) for n=0..19.

Christian Krattenthaler, Lattice path enumeration.  In: Handbook of Enumerative Combinatorics.  Edited by Miklos Bona.  CRC Press, 2015, pages 589-678.

FORMULA

G.f.: 2 - 1 / (Sum_{n>=0} binomial(4*n,2*n) * x^n).

Conjecture: a(n) = binomial(4*n,2*n) * (8*n+1) / (8*n^2 + 2*n - 1) for n >= 1.

PROG

(PARI) seq(n)={Vec(2 - 1/(O(x*x^n) + sum(k=0, n, binomial(4*k, 2*k)*x^k)))} \\ Andrew Howroyd, Aug 25 2020

CROSSREFS

Cf. A337291, A337292, A337351, A337352.

Sequence in context: A302148 A218685 A108432 * A245466 A284330 A125759

Adjacent sequences:  A337347 A337348 A337349 * A337351 A337352 A337353

KEYWORD

nonn,easy

AUTHOR

Lucas A. Brown, Aug 24 2020

STATUS

approved

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Last modified October 22 23:20 EDT 2021. Contains 348181 sequences. (Running on oeis4.)