What does the number next to a color mean?

Question

I'm reading this article about material design. In the list of colors, there is a number next to each color that seems to darken the color as its value goes up.

What does this number means, more precisely?

Edit: As all the answers are about the hex values, I'm adding this edit to clarify the question. My question is about the left hand side numbers like 700, 500, ... not the hex numbers (#3f51b5, ...)

Edit 2: In RGB model, each of the Red, Green or Blue can have a value in scale of 0 - 255. 0 means lack of the color and 255 means the color exists in full power. Is there a numerical meaning for the left hand side numbers? Can I calculate the '700' of a color, assuming '500' of it is #3F51B5? Or these numbers are just name for different shades of color in a palette?

Answer 1

Those values are the relative lightness/darkness or "tint" of the color, where 50 is lightest and 900 is darkest. The Material Design guidelines suggest using the 500 tint as your primary color and the 700 tint as the darker status bar color.

The Annn values are if you're using the color as your accent color.

See https://www.google.com/design/spec/style/color.html#color-ui-color-application