The two largest dismal-divisor counts among odd binary numbers

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Let d2(n)d_2(n) denote the number of dismal divisors of nn, and let nn range over the odd kk-digit binary numbers. Odd-binary divisor-count conjecture. The unique maximum of d2(n)d_2(n) occurs at

n=2k−1=111…111∣2.n=2^k-1=111\ldots111|_2.

If k≥3k\geq 3 and k≠5k\neq 5, the second-largest value occurs at

n=2k−3=111…101∣2,n=2^k-3=111\ldots101|_2,

and

n=2k−2k−2−1=101…111∣2,n=2^k-2^{k-2}-1=101\ldots111|_2,

possibly together with other values of nn. This refines the preceding binary maximum conjecture by restricting to odd numbers and specifying candidates for the second-largest value; the paper gives no proof or resolution.

References

Primary source

David Applegate, Marc LeBrun and N. J. A. Sloane, “Dismal Arithmetic”, arXiv:1107.1130 (2011).

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