Tuesday, December 2, 2008

47

47 is a safe prime number. A safe prime has the form 2p + 1, where p is also a prime.

There are 47 occurrences of 47 in the first thousand prime numbers.

43 + 73 = 407.

47 is the smallest number n for which 666n has a digit sum of 666.

The atomic number of silver is 47.

1 comment:

Lawrence said...

Long ago, I read that for n>47, a prime number always occurs between n and 9n/8--a much tighter range than shown by Erdos and Selberg (up to 2n). However, I don't remember the source nor have I seen either a proof or a refutation. (I admit I haven't tried very hard to check it) Can anyone confirm this statement (or give a counterexample)?