A q-congruence for the central trinomial coefficient

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Let pp be a prime with p≥5p\geq 5. Define the qq-analogue of the trinomial coefficient by

((nj))q=T1(n,j,q)=∑k=0nqk(k+j)(nk)q(n−kk+j)q,\left({n\choose j}\right)_q=T_1(n,j,q)=\sum_{k=0}^{n}q^{k(k+j)}{n\choose k}_q{n-k\choose k+j}_q,

where [n]q=(1−qn)/(1−q)[n]_q=(1-q^n)/(1-q) and ⌊x⌋\lfloor x\rfloor denotes the integral part of the real number xx. The q-congruence conjecture. One has

((2pp))q≡(2⌊p+36⌋+p)(qp−1)+2(mod[p]q2).\left(2p\choose p\right)_q\equiv\left(2\left\lfloor\frac{p+3}{6}\right\rfloor+p\right)(q^p-1)+2\pmod{[p]_q^2}.

This is proposed as a qq-analogue of the preceding trinomial congruence, motivated by numerical calculation; its validity is left as a problem for further research.

References

Primary source

Moa Apagodu and Ji-Cai Liu, “Congruence properties for the trinomial coefficients”, arXiv:1907.13547 (2019).

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