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A087403
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a(n) = smallest prime of the form 10*K(n) +1, where K is a number obtained by concatenation of n with itself, or 0 if no such prime exists.
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1
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11, 2221, 31, 41, 555555555551, 61, 71, 881, 991, 101, 1111111111111111111, 1212121, 131, 14141414141, 151, 1616161, 1717171717171717171717171717171, 181, 191, 20201, 211
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Conjecture: No term is zero.
Next term a(22) is too large (121 digits) to include in sequence. - Ray Chandler (rayjchandler(AT)sbcglobal.net), Sep 23 2003
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EXAMPLE
| a(2) = 2221 is a prime but 21 and 221 are composite.
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CROSSREFS
| Cf. A086766.
Sequence in context: A020519 A004822 A078271 * A085878 A064779 A138075
Adjacent sequences: A087400 A087401 A087402 * A087404 A087405 A087406
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KEYWORD
| base,nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Sep 10 2003
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