This site is supported by donations to The OEIS Foundation.

 Annual Appeal: Please make a donation to keep the OEIS running. In 2018 we replaced the server with a faster one, added 20000 new sequences, and reached 7000 citations (often saying "discovered thanks to the OEIS"). Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A068697 Smallest prime which is a concatenation of n consecutive odd numbers. If no such prime exists then 0. 0
 3, 13, 0, 23252729, 2527293133, 0, 57911131517, 4547495153555759, 0, 135791113151719, 87899193959799101103105107, 0, 23252729313335373941434547, 357911131517192123252729, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(3k) = 0. LINKS EXAMPLE a(4) = 23252729 as a concatenation of 23,25,27 and 29. a(3) = 0 for a concatenation of 3 odd numbers is always a multiple of 3. MATHEMATICA d[n_]:=IntegerDigits[n]; t={3}; Do[If[Mod[m, 3]==0, x=0, k=1; While[!PrimeQ[x=FromDigits[Fold[Join, d[k], Table[d[k+2n], {n, m-1}]]]], k++]]; AppendTo[t, x], {m, 2, 15}]; t (* Jayanta Basu, May 21 2013 *) CROSSREFS Cf. A052077. Sequence in context: A226129 A167368 A215240 * A010258 A107774 A253685 Adjacent sequences:  A068694 A068695 A068696 * A068698 A068699 A068700 KEYWORD base,hard,nonn AUTHOR Amarnath Murthy, Mar 03 2002 EXTENSIONS More terms from Sascha Kurz, Mar 26 2002 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 December 16 14:48 EST 2018. Contains 318167 sequences. (Running on oeis4.)