The binary-representation conjecture for fractional parts of binomial coefficients

Let p2p\neq 2 be a prime, let m=2pm=2p, and let mlml1m1m0m_lm_{l-1}\cdots m_1m_0 be the standard base-22 representation of mm. Let n1n\geq 1. Write n1n_1 for the leading digit in the base-pp representation of nn, let m0|m|_0 denote the number of zeros in the standard binary representation of mm, and let mod(a,b)\operatorname{mod}(a,b) be the unique integer xx with xa(modb)x\equiv a\pmod b and 0x<b0\leq x<b. Binary-representation conjecture. The quantity

2n(n2p)(p+1)(n11)pδpn\frac{2}{n}\binom{n}{2p}-\frac{(p+1)(n_1-1)}{p}\delta_{p\mid n}

is odd if and only if

n2p+i=0lj2mod(2p,2i+1)0δi=1mi2i(mod2log2(2p)+1)n\equiv 2p+\sum_{i=0}^l\left\lfloor\frac{j}{2^{|\operatorname{mod}(2p,2^{i+1})|_0-\delta_{i=1}}}\right\rfloor m_i2^i\pmod{2^{\lfloor\log_2(2p)\rfloor+1}}

for some 0j22p010\leq j\leq 2^{|2p|_0}-1. This criterion is intended to determine the fractional part of 1n(n2p)\frac{1}{n}\binom{n}{2p} from the binary representation of pp; its resolution is not given here.

Sources & referencesView supporting material

Primary source

Eric Rowland, “Two binomial coefficient conjectures”, arXiv:1102.1464 (2011).

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