Binomial-transform conjecture for classical and enhanced k-crossing-avoiding partitions

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For k≥2k\geq2, let Ck(n)C_k(n) be the number of partitions of [n][n] avoiding classical kk-crossings, and let Ek(n)E_k(n) be the number avoiding enhanced kk-crossings. Binomial-transform conjecture. Fix k≥2k\geq2. The following identity holds:

Ck(n+1)=∑i=0n(ni)Ek(i).C_k(n+1)=\sum_{i=0}^n{n\choose i}E_k(i).

The identity extends the known Catalan–Motzkin relation for k=2k=2 and the corresponding identity for k=3k=3. A proof is suggested as an open direction via bijections for crossing-avoiding partitions, and the source gives no resolution.

References

Primary source

Zhicong Lin, “Restricted inversion sequences and enhanced 3-noncrossing partitions”, arXiv:1706.07213 (2019).

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