Apéry congruence conjecture for the second-kind numbers modulo 99

For n0n\ge 0, define the Apéry numbers of the second kind by

An(3)=k=0n(nk)2(n+kk)2.A^{(3)}_n=\sum_{k=0}^n \binom{n}{k}^2\binom{n+k}{k}^2.

Write the ternary expansion of nn as a finite word over {0,1,2}\{0,1,2\}, and let kk be a nonnegative integer.

Second-kind Apéry congruence conjecture. The numbers An(3)A^{(3)}_n satisfy the following congruences modulo 99:

  1. An(3)1(mod9)A^{(3)}_n\equiv1\pmod 9 if and only if the ternary expansion of nn contains 6k6k digits equal to 11 for some kk, and otherwise contains only 00's and 22's.
  2. An(3)2(mod9)A^{(3)}_n\equiv2\pmod 9 if and only if the ternary expansion of nn contains 6k+56k+5 digits equal to 11 for some kk, and otherwise contains only 00's and 22's.
  3. An(3)4(mod9)A^{(3)}_n\equiv4\pmod 9 if and only if the ternary expansion of nn contains 6k+46k+4 digits equal to 11 for some kk, and otherwise contains only 00's and 22's.
  4. An(3)5(mod9)A^{(3)}_n\equiv5\pmod 9 if and only if the ternary expansion of nn contains 6k+16k+1 digits equal to 11 for some kk, and otherwise contains only 00's and 22's.
  5. An(3)7(mod9)A^{(3)}_n\equiv7\pmod 9 if and only if the ternary expansion of nn contains 6k+26k+2 digits equal to 11 for some kk, and otherwise contains only 00's and 22's.
  6. An(3)8(mod9)A^{(3)}_n\equiv8\pmod 9 if and only if the ternary expansion of nn contains 6k+36k+3 digits equal to 11 for some kk, and otherwise contains only 00's and 22's.
  7. In all other cases, An(3)A^{(3)}_n is divisible by 99; in particular, An(3)≢3,6(mod9)A^{(3)}_n\not\equiv3,6\pmod 9 for every nn.

As with the first-kind numbers, the relevant differential equation is not suitable for the paper's method. The patterns were obtained conjecturally modulo 99, and the supplied text gives no resolution.

Sources & referencesView supporting material

Primary source

Christian Krattenthaler and Thomas W. Müller, “A method for deterining the mod-3^k behaviour of recursive sequences”, arXiv:1308.2856 (2013).

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