metamath/valid/mathd-numbertheory-32.mm

$(
  @{
    @( (Contributed by Kunhao Zheng, 4-May-2021.) @)
    mathd-numbertheory-32 @p |- ( ph -> sum_ k e. { n e. NN | n || ; 3 6 } k = ; 9 1 ) @=
      ? @.
  @}
$)