A181371
identification: the entry's rule defines the sequence for every index; tail: the sequence is the entry's tail after some prefix rows; match_*: finite agreement only.
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A181371: Triangle read by rows: T(n,k) is the number of ternary words (i.e., finite sequences of 0's, 1's and 2's) of length n having k occurrences of 01's (0 <= k <= floor(n/2)).
(identification, match triangle)
A011973 → x ↦ (1/9)x−1/91 · 3 · 8, 1 · 21, 6 … row sums 1, 3, 9, 27, 81, 243, 729, 2187, …