This site is supported by donations to The OEIS Foundation.

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A102723 Smallest prime a(n) such that a(n)-x and a(n)+x, for x=1 to n, are all composite. 3
 5, 23, 23, 53, 53, 211, 211, 211, 211, 211, 211, 1847, 1847, 2179, 2179, 2179, 2179, 3967, 3967, 16033, 16033, 16033, 16033, 24281, 24281, 24281, 24281, 24281, 24281, 38501, 38501, 38501, 38501, 38501, 38501, 38501, 38501, 38501, 38501, 58831 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(2n+1)=a(2n). - Robert G. Wilson v, Feb 22 2005 Using Dirichlet's theorem, Sierpiński (1948) proved that a(n) exists for all n > 0. He noted that a(n) is a non-twin prime (A007510), except for a(1) = 5. - Jonathan Sondow, Oct 27 2017 LINKS W. Sierpiński, Remarque sur la répartition des nombres premiers, Colloq. Math., 1 (1948), 193-194. MATHEMATICA f[n_] := Block[{k = 1}, While[ Union[ PrimeQ /@ Sort[ Flatten[ Table[{Prime[k] - i, Prime[k] + i}, {i, n}]]]] != {False}, k++ ]; Prime[k]]; Table[ f[n], {n, 40}] (* Robert G. Wilson v, Feb 22 2005 *) CROSSREFS Cf. A007510, A023186. Sequence in context: A177242 A233756 A002582 * A136146 A289278 A167804 Adjacent sequences:  A102720 A102721 A102722 * A102724 A102725 A102726 KEYWORD nonn AUTHOR Ray G. Opao, Feb 06 2005 EXTENSIONS a(12)-a(40) from Robert G. Wilson v, Feb 22 2005 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.

Last modified January 19 20:33 EST 2019. Contains 319310 sequences. (Running on oeis4.)