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A261362 Least positive integer k such that both k and k*n belong to the set {m>0: 2*prime(prime(m))+1 = prime(p) for some prime p}. 3
2, 21531, 2, 35434, 11107, 35175, 24674, 64624, 127943, 1981, 155709, 50657, 74313, 11479, 6, 1981, 43405, 40859, 74229, 2, 154292, 51711, 29460, 29011, 42001, 28352, 2979, 85836, 6936, 186608, 3705, 14402, 25525, 96192, 6, 113433, 164, 787, 71873, 3365, 93169, 47219, 43128, 184740, 2, 78329, 13656, 6936, 139469, 26713 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Conjecture: Let a,b,c be positive integers with gcd(a,b) = gcd(a,c) = gcd(b,c) = 1. If a+b+c is even and a is not equal to b, then any positive rational number r can be written as m/n with m and n in the set {k>0: a*prime(p) - b*prime(prime(k)) = c for some prime p}.

This implies the conjecture in A261361.

REFERENCES

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.

LINKS

Zhi-Wei Sun, Table of n, a(n) for n = 1..2250

Zhi-Wei Sun, Checking the conjecture for (a,b,c) = (1,2,1) and r = s/t (s,t = 1..70)

Zhi-Wei Sun, Problems on combinatorial properties of primes, arXiv:1402.6641 [math.NT], 2014.

EXAMPLE

a(2) = 21531 since 2*prime(prime(21531))+1 = 2*prime(243799)+1 = 2*3403703+1 = 6807407 = prime(464351) with 464351 prime, and 2*prime(prime(21531*2))+1 = 2*prime(520019)+1 = 2*7686083+1 = 15372167 = prime(993197) with 993197 prime.

MATHEMATICA

f[n_]:=2*Prime[Prime[n]]+1

PQ[p_]:=PrimeQ[p]&&PrimeQ[PrimePi[p]]

Do[k=0; Label[bb]; k=k+1; If[PQ[f[k]]&&PQ[f[k*n]], Goto[aa], Goto[bb]]; Label[aa]; Print[n, " ", k]; Continue, {n, 1, 50}]

CROSSREFS

Cf. A000040, A005384, A260886, A261353, A261354, A261361.

Sequence in context: A242959 A123692 A290741 * A132942 A237521 A131558

Adjacent sequences:  A261359 A261360 A261361 * A261363 A261364 A261365

KEYWORD

nonn

AUTHOR

Zhi-Wei Sun, Aug 16 2015

STATUS

approved

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Last modified November 14 02:19 EST 2019. Contains 329108 sequences. (Running on oeis4.)