1,2

There are a lot of pp's such that 2*pp+1 is prime. On the contrary there are only two pp's < 10^6 such that (pp-1)/2 is prime: {27, 2187}.

2*A001597(n)+1.

8: 2*8+1=17 is prime.

Cf. A001597.

Sequence in context: A041915 A036764 A129548 this_sequence A041933 A041138 A048068

Adjacent sequences: A075076 A075077 A075078 this_sequence A075080 A075081 A075082

easy,nonn

Zak Seidov (zakseidov(AT)yahoo.com), Oct 11 2002