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A120628
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Primes such that their double is 1 away from a prime number.
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0
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2, 3, 5, 7, 11, 19, 23, 29, 31, 37, 41, 53, 79, 83, 89, 97, 113, 131, 139, 157, 173, 179, 191, 199, 211, 229, 233, 239, 251, 271, 281, 293, 307, 331, 337, 359, 367, 379, 419, 431, 439, 443, 491, 499, 509, 547, 577, 593, 601, 607, 619, 641, 653, 659, 661, 683
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| This sequence is a variation of the sequence in the reference. However this sequence should have an infinite number of terms.
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REFERENCES
| R. Crandall and C. Pomerance, Prime Numbers A Computational Perspective, Springer Verlag 2002, p. 49, exercise 1.18.
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EXAMPLE
| 19 is a prime and 19*2 = 38 which is one away from 37 which is prime.
13 is not in the table because 13*2 = 26 is one away from 25 and 27 both not
prime.
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MATHEMATICA
| Select[Range[683], PrimeQ[#] && Or[PrimeQ[2 # - 1], PrimeQ[2 # + 1]] &] (*Added by Ant King 12 Dec 2010*)
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PROG
| (PARI) primepm2(n, k) { local(x, p1, p2, f1, f2, r); if(k%2, r=2, r=1); for(x=1, n, p1=prime(x); p2=prime(x+1); if(isprime(p1*k+r)||isprime(p1*k-r), print1(p1", ") ) ) }
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CROSSREFS
| Cf. A005382, A005384.
Sequence in context: A069749 A081889 A078139 * A143260 A039986 A079346
Adjacent sequences: A120625 A120626 A120627 * A120629 A120630 A120631
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KEYWORD
| easy,nonn
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AUTHOR
| Cino Hilliard (hillcino368(AT)gmail.com), Aug 17 2006
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