login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A073703 Smallest prime p such that also p+prime(n)*2 is a prime. 16
3, 5, 3, 3, 7, 3, 3, 3, 7, 3, 5, 5, 7, 3, 3, 3, 13, 5, 3, 7, 3, 5, 7, 3, 3, 31, 5, 13, 5, 3, 3, 7, 3, 3, 13, 5, 3, 5, 3, 3, 31, 5, 7, 3, 3, 3, 11, 3, 3, 3, 13, 13, 5, 7, 7, 31, 3, 5, 3, 7, 3, 7, 3, 19, 5, 7, 11, 3, 7, 3, 3, 43, 5, 5, 3, 3, 19, 3, 7, 3, 19, 11, 19, 11, 3, 43, 13, 5, 7, 3, 3, 13, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

If Polignac's conjecture (1849) is correct, the sequence is defined for all n (as is A020483).

Also: least k-prime(n) such that k-prime(n) and k+prime(n) are both primes. - Pierre CAMI, Aug 27 2004

LINKS

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

EXAMPLE

n=5: prime(5)=11; 2+11*2=24, 3+11*2=25 and 5+11*2=27 are not prime, but 7+11*2=29 is prime, therefore a(5)=7.

MATHEMATICA

f[n_] := Block[{k = Prime[n], p = Prime[n]}, While[ !PrimeQ[k - p] || !PrimeQ[k + p], k++ ]; k - p]; Table[ f[n], {n, 95}] (* Robert G. Wilson v, Aug 28 2004 *)

PROG

(PARI) forprime(q=2, 500, forprime(p=2, default(primelimit), if(isprime(2*q+p), print1(p", "); next(2))); error("Not enough precomputed primes")) \\ Charles R Greathouse IV, Aug 21 2011

(Haskell)

a073703 n = head [p | p <- a000040_list, a010051 (p + 2 * a000040 n) == 1]

-- Reinhard Zumkeller, Oct 29 2013

CROSSREFS

Cf. A073704, A001747, A000040, A020483.

Cf. A010051.

Sequence in context: A124887 A304903 A097524 * A175019 A097519 A133773

Adjacent sequences:  A073700 A073701 A073702 * A073704 A073705 A073706

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Aug 04 2002

EXTENSIONS

Merged with Pierre CAMI's submission of Aug 2004 - R. J. Mathar, Jul 29 2008

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 23 23:51 EDT 2019. Contains 328379 sequences. (Running on oeis4.)