Bernoulli-denominator conjecture for Toda-prime sets

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For an even integer 2m2m, let P(2m)P(2m) be the set of primes pp such that p−1∣2mp-1\mid 2m, so that

D2m=∏p∈P(2m)p,D_{2m}=\prod_{p\in P(2m)}p,

where D2mD_{2m} is the denominator of the Bernoulli number B2mB_{2m}. Let F(d)=min⁡{2m>0:D2m=d}F(d)=\min\{2m>0:D_{2m}=d\}. Also let T(n)T(n) be the set of Toda primes of nn, and write t(n)=∣T(n)∣t(n)=|T(n)|. Bernoulli-denominator conjecture. Let dd be a Bernoulli denominator.

(i) If F(d)=4aF(d)=4a for some integer aa, then T(am)=T(a)T(am)=T(a) whenever D4am=D4aD_{4am}=D_{4a}.

(ii) If D4am≠D4a=dD_{4am}\neq D_{4a}=d, then t(am)≥t(a)t(am)\geq t(a).

The conjecture proposes that equality or growth of Bernoulli denominators controls the Toda-prime sets and their cardinalities. It extends several case-by-case propositions proved or stated earlier in the paper; its general validity is left open.

References

Primary source

Stephen McKean, “Toda primes”, arXiv:2511.19744 (2025).

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