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A070278
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Smallest prime > 2n+1 beginning and ending with 2n+1, or 0 if no such prime exists.
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2
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11, 313, 0, 727, 919, 11311, 13313, 0, 17117, 19219, 21121, 23623, 0, 27127, 29129, 31231, 33533, 0, 37337, 39139, 41141, 43543, 0, 47147, 49549, 51151, 53353, 0, 57457, 59159, 61261, 63463, 0, 67567, 692269, 71171, 73673, 0, 77377, 79279
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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COMMENTS
| No such prime exists if n is even or divisible by 5. It is not until n = 69 that it necessary to insert more than one digit. The next few examples are 99, 101, 103, 123, 157, 181 & 199.
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MATHEMATICA
| f[n_] := Block[{a = IntegerDigits[n]}, If[ Mod[n, 5] == 0, Return[0], If[ p = FromDigits[ Join[a, a]]; PrimeQ[p], Return[p], k = 0; While[p = FromDigits[ Join[a, IntegerDigits[k], a]]; !PrimeQ[p], k++ ]]; p]]; Table[ f[n], {n, 1, 89, 2}]
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CROSSREFS
| Sequence in context: A193890 A185071 A060495 * A090272 A090271 A106827
Adjacent sequences: A070275 A070276 A070277 * A070279 A070280 A070281
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KEYWORD
| base,nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), May 07 2002
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EXTENSIONS
| Edited by N. J. A. Sloane (njas(AT)research.att.com), Vladeta Jovovic (vladeta(AT)eunet.rs) and Robert G. Wilson v (rgwv(AT)rgwv.com), May 09 2002
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