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A087919 Indices for which there is at least one twin prime pair between two consecutive prime-indexed primes. 0
1, 2, 3, 4, 6, 7, 8, 9, 11, 13, 14, 15, 16, 17, 18, 19, 22, 23, 24, 25, 27, 29, 30, 34, 36, 39, 40, 42, 46, 47, 48, 50, 51, 54, 55, 56, 59, 61, 62, 63, 65, 66, 67, 68, 71, 74, 76, 77, 78, 79, 82, 86, 88, 90, 91, 92, 94, 95, 97, 99, 100, 101, 102, 103, 105, 106, 107, 110, 111 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

It is not known whether there will always be instances where no twin prime pair exists between two consecutive prime-indexed primes.

LINKS

Table of n, a(n) for n=1..69.

FORMULA

x such that prime(prime(x)) and prime(prime(x+1)) contain a twin prime pair.

EXAMPLE

Prime(4)=17, prime(5)=31. Between 17 and 31 are two twin prime pairs: 17,19 and 29,31. prime(5) -> prime(6) = 31 -> 41 contain no twin prime pairs so 5 is not in the sequence.

PROG

(PARI) piptwins(n) = { for(x=1, n, f=0; p1 = prime(prime(x)); p2 = prime(prime(x+1)); for(y=p1, p2, if(isprime(y) && y+2 <= p2 && isprime(y+2), print1(x", "); break) ) ) }

CROSSREFS

Sequence in context: A194463 A140467 A103677 * A113508 A059325 A258938

Adjacent sequences:  A087916 A087917 A087918 * A087920 A087921 A087922

KEYWORD

nonn

AUTHOR

Cino Hilliard, Oct 26 2003

STATUS

approved

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Last modified July 18 21:25 EDT 2019. Contains 325144 sequences. (Running on oeis4.)