1,1

The ratio of successive terms appears to converge. They are as follows for n = 2 to 6:

n pip(10^n)/pip(10^(n-1))

-- ----------------------------

2 4.625000000000000000000000000

3 6.756756756756756756756756757

4 8.132000000000000000000000000

5 8.420560747663551401869158878

6 8.458145919738302470938723056

Here prime(n) is the n-th prime number, pip(n) = prime(prime(n)) is the n-th prime-index-prime.

The first 10^1 prime-index-primes are 3,5,11,17,31,41,59,67,83,109. The 8 primes 3,5,11,17,31,41,59,109 are also twin prime members. So 8 is the first entry in the table.

(PARI) g(n) = c=0; for(x=1, n, y=prime(prime(x)); if(isprime(y+2)||isprime(y-2), c++)); c

Sequence in context: A055799 A035038 A111645 this_sequence A163832 A139798 A065762

Adjacent sequences: A128243 A128244 A128245 this_sequence A128247 A128248 A128249

more,nonn

Cino Hilliard (hillcino368(AT)hotmail.com), May 09 2007