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Search: id:A066065
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| A066065 |
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a(n) = smallest prime q such that in decimal notation the concatenation prime(n)q yields a prime ( = A066064(n)). |
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+0
2
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| 3, 7, 3, 3, 3, 7, 3, 3, 3, 3, 3, 3, 11, 3, 23, 23, 3, 3, 3, 29, 3, 7, 11, 23, 7, 3, 3, 11, 3, 11, 7, 47, 3, 13, 3, 31, 31, 7, 29, 3, 11, 19, 3, 3, 3, 3, 3, 7, 3, 3, 3, 3, 7, 11, 17, 3, 3, 3, 7, 11, 3, 11, 13, 23, 7, 23, 3, 3, 29, 13, 3, 3, 3, 3, 3, 3, 17, 19, 3, 3, 11, 7, 17, 7, 7, 71, 3, 37, 41
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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a(k) < prime(k) for k > 2.
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LINKS
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Harry J. Smith, Table of n, a(n) for n=1,...,1000
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EXAMPLE
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A000040(13) = 41; for the first four primes 2, 3, 5 and 7 we get 412, 413, 415 and 417, which are all composite, but with the 5th prime we have 4111 = A066064(13), so a(13) = 11.
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PROGRAM
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(PARI) digitsIn(x)= { local(d); if (x==0, return(1)); d=1 + log(x)\log(10); if (10^d == x, d++, if (10^(d-1) > x, d--)); return(d) } Concat(a, b)= { return(a*10^digitsIn(b) + b) } { for (n = 1, 1000, p=prime(n); q=2; while(!isprime(Concat(p, q)), q=nextprime(q + 1)); write("b066065.txt", n, " ", q) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Nov 09 2009]
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CROSSREFS
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Sequence in context: A135613 A019973 A010623 this_sequence A145511 A065443 A117190
Adjacent sequences: A066062 A066063 A066064 this_sequence A066066 A066067 A066068
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KEYWORD
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base,nonn,new
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AUTHOR
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Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Dec 01 2001
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