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A260208
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Least prime p such that 2p*n+1 = prime(q*n) for some prime q.
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1
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2, 3, 2, 107, 271, 3, 3, 523, 17, 191, 73, 2707, 587, 2017, 19, 233, 57193, 7583, 9791, 7, 2111, 1373, 43, 109, 1283, 463, 8179, 25583, 7489, 1733, 9011, 7753, 7853, 887, 10141, 71, 1373, 7927, 509, 1433, 4513, 2399, 4211, 26407, 307, 2843, 58579, 3121, 5519, 38371
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OFFSET
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1,1
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COMMENTS
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Conjecture: a(n) exists for any n > 0. In general, if a > 0 is even and b is 1 or -1, then for any positive integer n there are primes p and q such that a*p*n+b = prime(q*n).
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REFERENCES
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Zhi-Wei Sun, Problems on combinatorial properties of primes, in: M. Kaneko, S. Kanemitsu and J. Liu (eds.), Number Theory: Plowing and Starring through High Wave Forms, Proc. 7th China-Japan Seminar (Fukuoka, Oct. 28 - Nov. 1, 2013), Ser. Number Theory Appl., Vol. 11, World Sci., Singapore, 2015, pp. 169-187.
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LINKS
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EXAMPLE
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a(5) = 271 since 2*271*5+1 = 2711 = prime(79*5) with 271 and 79 both prime.
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MATHEMATICA
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PQ[n_, p_]:=PrimeQ[p]&&PrimeQ[PrimePi[p]/n]
Do[k=0; Label[aa]; k=k+1; If[PQ[n, 2*Prime[k]*n+1]], Goto[bb], Goto[aa]]; Label[bb]; Print[n, " ", Prime[k]]; Continue, {n, 1, 50}]
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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