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arxiv: 1706.07064 · v2 · pith:CW6CKQFCnew · submitted 2017-06-21 · 🧮 math.CO

A New Quantity Counted by OEIS Sequence A006012

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keywords sequencea006012avoidingconjecturecountedcountsdefinedexisting
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We prove an existing conjecture that the sequence defined recursively by $a_1=1, a_2=2, a_n=4a_{n-1}-2a_{n-2}$ counts the number of length-$n$ permutations avoiding the four generalized permutation patterns 1-32-4, 1-42-3, 2-31-4, and 2-41-3.

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