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 A087920 Indices for which there is no twin prime pair between two consecutive prime-indexed primes. 0

%I

%S 5,10,12,20,21,26,28,31,32,33,35,37,38,41,43,44,45,49,52,53,57,58,60,

%T 64,69,70,72,73,75,80,81,83,84,85,87,89,93,96,98,104,108,109,113,116,

%U 118,120,124,126,130,134,140,142,143,147,152,155,159,163,164,165,169,171

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

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

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

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

%o (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",")) ) }

%K nonn

%O 1,1

%A _Cino Hilliard_, Oct 26 2003

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Last modified August 12 10:16 EDT 2022. Contains 356069 sequences. (Running on oeis4.)