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

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

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 December 15 20:00 EST 2019. Contains 330000 sequences. (Running on oeis4.)