A087919 Indices for which there is at least one twin prime pair between two consecutive prime-indexed primes.

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

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