A001818
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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A204420: Triangle T(n,k) giving number of degree-2n permutations which decompose into exactly k cycles of even length, k=0..n.
(match row sums)
1 · 0, 1 · 0, 6, 3 · 0, 120, 90, 15 … row sums 1, 1, 9, 225, 11025, 893025, 108056025, …