

A247895


Least integer k > 0 such that prime(k)  k*n is prime.


3



3, 7, 13, 31, 69, 190, 444, 1052, 2702, 6455, 15928, 40073, 100370, 251707, 637321, 1617175, 4124448, 10553415, 27066978, 69709680, 179992909, 465769803, 1208198532, 3140421716, 8179002120, 21338685408, 55762149030, 145935689361, 382465573486, 1003652347100
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OFFSET

1,1


COMMENTS

Conjecture: (i) a(n) exists for any n > 0.
(ii) For each integer n > 2, there is a positive integer k with k*n  prime(k) prime.


LINKS

Giovanni Resta, Table of n, a(n) for n = 1..50
ZhiWei Sun, A new theorem on the primecounting function, arXiv:1409.5685 [math.NT], 20142017.


EXAMPLE

a(1) = 3 since prime(3)  3*1 = 5  3 = 2 is prime.


MATHEMATICA

Do[k=1; Label[aa]; If[Prime[k]>k*n&&PrimeQ[Prime[k]k*n], Print[n, " ", k]; Goto[bb]]; k=k+1; Goto[aa]; Label[bb]; Continue, {n, 1, 22}]


CROSSREFS

Cf. A000040, A247278, A247793.
Sequence in context: A220746 A110436 A126879 * A336688 A155128 A176589
Adjacent sequences: A247892 A247893 A247894 * A247896 A247897 A247898


KEYWORD

nonn


AUTHOR

ZhiWei Sun, Sep 28 2014


EXTENSIONS

Terms a(23) and beyond from Giovanni Resta, Apr 22 2020


STATUS

approved



