Depending on the font and the syntax highlighting scheme, some letters look a lot like numbers. In some configurations, for example,
l (lower case
1 (one) are basically indistinguishable. Github, for instance, while not the worst offender, isn’t doing a great job there.
List(1, 11, 111, 111l, 11111, 11111, 11111)
Using upper-case letters makes this more obvious:
List(1, 11, 111, 111L, 11111, 11111, 11111)