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A New Sequence Counted by OEIS Sequence A006012. (arXiv:1706.07064v1 [math.CO])

来源于:arXiv
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. 查看全文>>