%N Prime numbers n for which the number of prime numbers smaller than n is also a prime number.
%F a(n) = prime(1 + prime(n)). - T. D. Noe, April 05 2011
%e 163 is in the sequence because (1) it is a prime number, (2) there are 37 prime numbers smaller than 163 and 37 is also a prime number.
%t Prime[1 + Prime[Range]] (* From Harvey P. Dale, Apr 05 2011 *)
%Y Cf. A000720.
%A Luc Stevens (lms022(AT)yahoo.com), Apr 23 2006
%E Corrected and extended by Harvey P. Dale, Apr 05 2011.