21 1 x 2 7 July 8, 2019 16 32 64 128 21 x 2 1 3 1 7 21 1 2 x 19 7 8 x 1 21 1 2 x 19 7 8 filter 7 1 x 2 21 as a fraction 1 2 x 7 28 21 1 2 x 72 x 21 19 7 8 x 21 1 2 x 3 4 1 2 x 22 7 x 21 21x1 7 21 x 7