A087920 Indices for which there is no twin prime pair between two consecutive prime-indexed primes.

5, 10, 12, 20, 21, 26, 28, 31, 32, 33, 35, 37, 38, 41, 43, 44, 45, 49, 52, 53, 57, 58, 60, 64, 69, 70, 72, 73, 75, 80, 81, 83, 84, 85, 87, 89, 93, 96, 98, 104, 108, 109, 113, 116, 118, 120, 124, 126, 130, 134, 140, 142, 143, 147, 152, 155, 159, 163, 164, 165, 169, 171

Offset

1,1

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..62.

Formula

x such that prime(prime(x)) and prime(prime(x+1)) contain no twin prime pair.

Example

Prime(5) -> prime(6) = 31 -> 41 contains no twin prime pairs, so 5 is in the sequence.

Prog

(PARI) piptwins2(n) = { for(x=1, n, f=1; p1 = prime(prime(x)); p2 = prime(prime(x+1)); for(y=p1, p2, if(isprime(y) && y+2 <= p2 && isprime(y+2), f=0) ); if(f, print1(x", ")) ) }

Crossrefs

Sequence in context: A313370 A313371 A313372 * A313373 A313374 A103676

Adjacent sequences: A087917 A087918 A087919 * A087921 A087922 A087923

Keyword

nonn

Author

Cino Hilliard, Oct 26 2003

Status

approved