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Irregular tree read by rows: take the Stern-Brocot tree A007305(n)/A007306(n) and set a(n) = A007306(n) - A007305(n) mod 3.
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%I #23 Aug 05 2020 14:15:54

%S 1,0,1,2,1,0,0,2,1,1,2,2,1,0,0,2,1,2,1,2,1,1,2,1,2,1,2,2,1,0,0,2,1,0,

%T 0,2,1,2,1,0,0,0,0,1,2,1,2,0,0,2,1,2,1,1,2,1,2,1,2,2,1,0,0,2,1,1,2,2,

%U 1,0,0,2,1,2,1,0,0,2

%N Irregular tree read by rows: take the Stern-Brocot tree A007305(n)/A007306(n) and set a(n) = A007306(n) - A007305(n) mod 3.

%H Kiana Mittelstaedt, <a href="https://arxiv.org/abs/1902.03195">A Stochastic Approach to Eulerian Numbers</a>, arXiv:1902.03195 [math.CO], 2019. Also Amer. Math. Mnthly, 127:7 (2020), 618-628. See Fig. 5. Note that this author has omitted the two initial terms.

%e The initial rows of the tree are 1,0 // 1 // 2,1 // 0,0,2,1 // 1,2,2,1,0,0,2,1 // ...

%Y Cf. A002487, A007305, A007306, A049448, A049449, A057431.

%K nonn,tabf

%O 0,4

%A _N. J. A. Sloane_, Aug 05 2020