

A136020


Smallest prime of the form (2*n+1)*prime(k)2*n, any k.


57



7, 11, 29, 19, 23, 53, 31, 103, 191, 43, 47, 101, 109, 59, 311, 67, 71, 149, 79, 83, 173, 181, 283, 197, 103, 107, 331, 229, 709, 367, 127, 131, 269, 139, 853, 293, 151, 463, 317, 163, 167, 1021, 349, 179, 547, 373, 191, 389, 199, 607, 619, 211, 643, 1091, 223
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OFFSET

1,1


COMMENTS

The associated prime(k) are in A136019.


LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000


EXAMPLE

a(1)=7 because 7 is smallest prime p such that (p+2)/3 is prime
a(2)=11 because 11 is smallest prime p such that (p+4)/5 is prime
a(3)=29 because 29 is smallest prime p such that (p+6)/7 is prime


MATHEMATICA

a = {}; Do[k = 1; While[ !PrimeQ[(Prime[k] + 2n)/(2n + 1)], k++ ]; AppendTo[a, Prime[k]], {n, 1, 100}]; a
Reap[Do[k = PrimePi[2n+1]; While[ !PrimeQ[((p=Prime[k]) + 2n)/(2n + 1)], k++ ]; Sow[p], {n, 100}]][[2, 1]] (* Zak Seidov, Mar 04 2013 *)


PROG

(PARI) a(n)=my(t); n+=n; forprime(p=2, default(primelimit), if(isprime(t=(n+1)*pn), return(t))) \\ Charles R Greathouse IV, Feb 13 2011


CROSSREFS

Cf. A136019, A136026, A136027.
Sequence in context: A158807 A338929 A067006 * A076304 A122560 A136338
Adjacent sequences: A136017 A136018 A136019 * A136021 A136022 A136023


KEYWORD

nonn,easy


AUTHOR

Artur Jasinski, Dec 10 2007


EXTENSIONS

Edited by R. J. Mathar, May 17 2009


STATUS

approved



