That's a verrrrrry interesting number !
It belongs to an infinite number of sets,
and I'm pretty busy right now.
Here are just a few of them:
-- real numbers
-- rational numbers
-- positive numbers
-- mixed numbers
-- multiples of 0.1
-- multiples of 0.2
-- multiples of 0.3
-- multiples of 0.4
-- multiples of 0.6
-- multiples of 0.8
-- multiples of 0.9
-- multiples of 1.2
-- numbers less than 7.21
-- numbers less than 7.22
-- numbers less than 7.23
.
.
etc.
-- numbers greater than 7.19
-- numbers greater than 7.18
-- numbers greater than 7.17
.
.
etc.