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Search: id:A073640
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| A073640 |
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a(1) = 2; a(n) = smallest prime greater than the previous term such that concatenation of two successive terms is a prime. |
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+0
7
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| 2, 3, 7, 19, 31, 37, 61, 73, 127, 139, 199, 211, 229, 283, 397, 433, 439, 463, 523, 541, 547, 577, 601, 607, 619, 739, 751, 787, 811, 919, 937, 991, 1009, 1021, 1039, 1093, 1201, 1213, 1297, 1447, 1453, 1459, 1471, 1483, 1657, 1663, 1723, 1783, 1867, 1879
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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e.g. a(1)=2, the next prime is 3 and when 2 and 3 are concatenated we get 23, another prime. Hence a(2)=3. Likewise, a(3)=7 because 37 is prime, whereas the next prime after 3 is "5" which would lead to the nonprime "35".
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MAPLE
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pout := [2]: nout := [1]: for n from 2 to 1000 do: p := ithprime(n): d := parse(cat(pout[nops(pout)], p)): if (isprime(d)) then pout := [op(pout), p]: nout := [op(nout), n]: fi: od:
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CROSSREFS
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Sequence in context: A040112 A074855 A038935 this_sequence A005382 A113165 A128025
Adjacent sequences: A073637 A073638 A073639 this_sequence A073641 A073642 A073643
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KEYWORD
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base,nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Aug 09 2002
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EXTENSIONS
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More terms from Mark Hudson (mrmarkhudson(AT)hotmail.com), Jan 31 2003
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