A335340 - OEIS

%I #13 Feb 09 2021 21:00:34

%S 2,4,2,6,12,2,8,36,24,2,10,80,120,40,2,12,150,400,300,60,2,14,252,

%T 1050,1400,630,84,2,16,392,2352,4900,3920,1176,112,2,18,576,4704,

%U 14112,17640,9408,2016,144,2,20,810,8640,35280,63504,52920,20160,3240,180,2

%N North-East paths from (0,0) to (n,n) with k cyclic descents.

%C A North-East path is a path from (0,0) to (n,n) using steps (1,0) and (0,1). A cyclic descent is a North step followed by an East step, where the last and first step is a cyclic descent if the path ends with a North step and starts with an East step.

%C The sum of the entries in row n is equal to binomial(2n,n).

%C I conjecture that the polynomial Sum_{k=1...n} T(n,k) t^k is real-rooted for all n.

%H Per Alexandersson, Svante Linusson, Samu Potka, and Joakim Uhlin, <a href="https://arxiv.org/abs/2010.11157">Refined Catalan and Narayana cyclic sieving</a>, arXiv:2010.11157 [math.CO], 2020.

%F T(n,k) = 2*binomial(n,k)*binomial(n-1,k-1).

%F T(n,k) = 2 * A103371(n-1,k-1). - _Alois P. Heinz_, Jun 02 2020

%e The table starts as

%e 2,

%e 4, 2

%e 6, 12, 2

%e 8, 36, 24, 2

%e 10, 80, 120, 40, 2

%e 12, 150, 400, 300, 60, 2

%t T[n_, k_] = 2 Binomial[n, k] Binomial[n - 1, k - 1];

%Y Cf. A103371.

%K nonn,tabl

%O 1,1

%A _Per W. Alexandersson_, Jun 02 2020