{1, 2, 3, 4, 5}
{1, 3, 6, 10, 15, 21, 28, 36, 45}
⟅1, 2, 3, 4, 5⟆
⟅1, 3, 6, 10, 15, 21, 28, 36, 45⟆
"abcdefghijklmnopqrstuvwxyz"