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A087920 Indices for which there is no twin prime pair between two consecutive prime-indexed primes. 0
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified June 26 21:14 EDT 2022. Contains 354885 sequences. (Running on oeis4.)