In the first decade of numbers (1-10), there are four prime numbers (2,3,5,7). In the second decade (11-20), there are another four (11,13,17,19).

Are there other such decades with four prime numbers?

Yes.

some examples:
101, 103, 107, 109
191, 193, 197, 199
821, 823, 827, 829

(found using the online dictionary of integer sequences)

Posted by Robby Goetschalckx on 2006-11-06 08:22:12