Trailing Betti numbers for Sally type semigroups S^e(m)

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Fix the multiplicity ee and write βj(m):=βj(Se(m))\beta_j(m):=\beta_j(S^e(m)). Trailing Betti-number conjecture. For every m≥2m\geq 2, the Betti numbers satisfy

βj(1)=βj(m)for all j≤m−2,\beta_j(1)=\beta_j(m)\quad\text{for all }j\leq m-2,

and

βj(m)=βj(1)+(e−mj+1−m)for m−1≤j≤e−2.\beta_j(m)=\beta_j(1)+\binom{e-m}{j+1-m}\quad\text{for }m-1\leq j\leq e-2.

This proposes that the Betti sequence of Se(m)S^e(m) agrees initially with that of the Gorenstein semigroup Se(1)S^e(1) and then differs by the displayed correction term; the status of the formula is not resolved in the supplied text.

References

Primary source

Kriti Goel, Nil Şahin, Srishti Singh and Hema Srinivasan, “Numerical Semigroups of Sally Type II”, arXiv:2512.10812 (2025).

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