Alternate bottom on :nth-child(3n + 1)

Sequence repeats every 6 items, alternate bottom on 33.34% of shapes

Alternate bottom on :nth-child(3n + 1), :nth-child(5n + 1)

Sequence repeats every 30 items, alternate bottom on 46.67% of shapes

Alternate bottom on :nth-child(3n + 1), :nth-child(5n + 1), child(7n + 1)

Sequence repeats every 210 items, alternate bottom on 52.38% of shapes