The two largest dismal-divisor counts among odd binary numbers

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=2k1=1111112.n=2^k-1=111\ldots111|_2.

If k3k\geq 3 and k5k\neq 5, the second-largest value occurs at

n=2k3=1111012,n=2^k-3=111\ldots101|_2,

and

n=2k2k21=1011112,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.

Sources & referencesView supporting material

Primary source

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

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