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A246810 a(n) is the smallest number m such that np(m) = n, where np(m) is number of primes p such that prime(m) < p < prime(m)^(1 + 1/m). 5
1, 5, 12, 17, 25, 55, 83, 169, 207, 206, 384, 953, 1615, 2192, 2197, 3024, 3023, 10709, 10935, 29509, 29508, 62736, 62735, 94333, 94332, 196966, 314940, 608777, 1258688, 1767259, 2448975, 2448973, 7939362, 9373136, 9373134, 16854966, 16854967 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Firoozbakht's conjecture says that for every n, there exists at least one prime p where, prime(n) < p < prime(n)^(1 + 1/n). Hence if Firoozbakht's conjecture is true, then there is no m such that np(m) = 0.

Conjecture: For every positive integer n, a(n) exists.

a(65) > 10^12. - Robert Price, Nov 12 2014

LINKS

Robert Price, Table of n, a(n) for n = 1..64

A. Kourbatov, Verification of the Firoozbakht conjecture for primes up to four quintillion, arXiv:1503.01744 [math.NT], 2015

A. Kourbatov, Upper bounds for prime gaps related to Firoozbakht's conjecture, J. Int. Seq. 18 (2015) 15.11.2

Nilotpal Kanti Sinha, On a new property of primes that leads to a generalization of Cramer's conjecture, arXiv:1010.1399v2 [math.NT], 2010.

Wikipedia, Firoozbakht's conjecture.

EXAMPLE

a(6) = 55 since the number of primes p such that prime(55) < p < prime(55)^(1 + 1/55) is 6 and 55 is the smallest number with this property.

MATHEMATICA

np[n_]:=(b=Prime[n]; Length[Select[Range[b+1, b^(1 + 1/n)], PrimeQ]]); a[n_]:=(For[m=1, np[m] !=n, m++]; m);

Do[Print[a[n]], {n, 37}]

CROSSREFS

Cf. A000040, A182134, A246781, A246782, A246783, A246787.

Sequence in context: A214067 A290494 A246787 * A063297 A237669 A022137

Adjacent sequences:  A246807 A246808 A246809 * A246811 A246812 A246813

KEYWORD

nonn

AUTHOR

Farideh Firoozbakht and Jahangeer Kholdi, Oct 10 2014

STATUS

approved

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Last modified June 19 05:14 EDT 2021. Contains 345125 sequences. (Running on oeis4.)