var example = '9_000_000_000'
var example2 = '9_000_000_000xx'
var regex1 = /^\d(?:_?\d)*n/
var regex2 = /^\d+(?:_\d+)*n/
var regex3 = /^\d+(?:_?\d)*n/example.match(regex1)
example2.match(regex1)example.match(regex2)
example2.match(regex2)example.match(regex3)
example2.match(regex3)