

A235592


Numbers k such that k*(k+1)  prime(k) is prime.


11



2, 3, 4, 5, 6, 8, 9, 11, 14, 15, 18, 19, 20, 21, 26, 27, 29, 34, 36, 37, 38, 41, 44, 45, 48, 53, 54, 57, 61, 62, 69, 70, 71, 85, 86, 87, 89, 90, 98, 99, 102, 105, 112, 114, 117, 119, 131, 134, 135, 136, 137, 141, 145, 147, 149, 150, 153, 156, 157, 162, 170, 171, 175, 176, 180, 183, 187, 189, 198, 200
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OFFSET

1,1


COMMENTS

It is known that prime(k) <= k*(k+1) for any positive integer k. The conjecture in A235613 implies that the sequence has infinitely many terms.
Conjecture: This sequence contains infinitely many primes.


LINKS

ZhiWei Sun, Table of n, a(n) for n = 1..10000


EXAMPLE

a(1) = 2 since 1*2  prime(1) = 0 is not prime, but 2*3  prime(2) = 3 is prime.
a(2) = 3 since 3*4  prime(3) = 7 is prime.
a(3) = 4 since 4*5  prime(4) = 13 is prime.


MATHEMATICA

n=0; Do[If[PrimeQ[k(k+1)Prime[k]], n=n+1; Print[n, " ", k]], {k, 1, 200}]


CROSSREFS

Cf. A000040, A235613, A235614.
Sequence in context: A177738 A134030 A226189 * A100054 A101271 A093110
Adjacent sequences: A235589 A235590 A235591 * A235593 A235594 A235595


KEYWORD

nonn


AUTHOR

ZhiWei Sun, Jan 12 2014


STATUS

approved



