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 A128246 Number of twin prime members occurring in the sequence of prime-index-primes for indices up to 10^n. 0
 8, 37, 250, 2033, 17119, 144795 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 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 LINKS FORMULA Here prime(n) is the n-th prime number, pip(n) = prime(prime(n)) is the n-th prime-index-prime. EXAMPLE 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. PROG (PARI) g(n) = c=0; for(x=1, n, y=prime(prime(x)); if(isprime(y+2)||isprime(y-2), c++)); c CROSSREFS Sequence in context: A221063 A221633 A201452 * A204076 A163832 A139798 Adjacent sequences:  A128243 A128244 A128245 * A128247 A128248 A128249 KEYWORD more,nonn AUTHOR Cino Hilliard (hillcino368(AT)hotmail.com), May 09 2007 STATUS approved

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