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A275021
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Pairs of primes p, p+4 such that p-2 and p+6 are composite.
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2
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79, 83, 127, 131, 163, 167, 379, 383, 397, 401, 439, 443, 487, 491, 499, 503, 673, 677, 739, 743, 757, 761, 769, 773, 907, 911, 937, 941, 967, 971, 1009, 1013, 1213, 1217, 1549, 1553, 1567, 1571, 1579, 1583, 1597, 1601, 2203, 2207, 2293, 2297
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OFFSET
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1,1
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COMMENTS
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List of prime numbers that occur in pairs of the form {p, p+4} after the sequential removal, from a list of all the primes, of (1) the one pair of primes of the form {p, p+1}, (2) all remaining twin prime pairs {p, p+2}.
Conjecture: the sequence has infinitely many terms and the sum of their reciprocals converges.
The second half of the conjecture is correct. The first half is true on Dickson's conjecture (because, for example, it would show that there are infinitely many k such that 210k+127 and 210k+131 are both prime). - Charles R Greathouse IV, Nov 20 2016
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LINKS
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PROG
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(PARI) {
/* For biggest n allocatemem(max)*/
n=10^4-1;
v=vector(n, unused, 1);
for(i=2, sqrt(n),
if(v[i],
forstep(j=i^2, n, i, v[j]=0))
);
v[2]=0; v[3]=0;
for(i=5, n-2,
if(v[i]&&v[i+2],
v[i]=0; v[i+2]=0
)
);
for(i=5, n-4,
if(v[i]&&v[i+4],
print1(i", "i+4", ");
v[i]=0; v[i+4]=0;
)
)
}
(PARI) p=2; q=3; r=5; forprime(s=7, 1e3, if(r-q==4 && q-p>2 && s-r>2, print1(q", "r", ")); p=q; q=r; r=s) \\ Charles R Greathouse IV, Nov 19 2016
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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