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A071620
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Integer lengths of the Champernowne primes (concatenation of first a(n) entries (digits) of A033307 is prime).
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5
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OFFSET
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1,1
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COMMENTS
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Next term has n > 113821. - Eric W. Weisstein, Nov 04 2015
Also: concatenation of A007376(1 .. a(n)) is prime. - M. F. Hasler, Oct 23 2019
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LINKS
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Table of n, a(n) for n=1..7.
Eric Weisstein's World of Mathematics, Champernowne Constant Digits
Eric Weisstein's World of Mathematics, Consecutive Number Sequences
Eric Weisstein's World of Mathematics, Constant Primes
Eric Weisstein's World of Mathematics, Integer Sequence Primes
Eric Weisstein's World of Mathematics, Smarandache Prime
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MATHEMATICA
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f[0] = 0; f[n_Integer] := 10^(Floor[Log[10, n]] + 1)*f[n - 1] + n; Do[If[PrimeQ[FromDigits[Take[IntegerDigits[f[n]], n]]], Print[n]], {n, 1, 3000}]
Cases[FromDigits /@ Rest[FoldList[Append, {}, RealDigits[N[ChampernowneNumber[], 1000]][[1]]]], p_?PrimeQ :> IntegerLength[p]] (* Eric W. Weisstein, Nov 04 2015 *)
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CROSSREFS
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Cf. A007376 (infinite Barbier word = almost-natural numbers: write n in base 10 and juxtapose digits).
Cf. A033307 (decimal expansion of Champernowne constant), A176942 (the corresponding primes of length a(n)), A265043.
Cf. A072125.
Sequence in context: A069207 A168671 A136197 * A175664 A053690 A177948
Adjacent sequences: A071617 A071618 A071619 * A071621 A071622 A071623
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KEYWORD
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nonn,base,hard,more
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AUTHOR
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Robert G. Wilson v, Jun 21 2002
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EXTENSIONS
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Edited by Charles R Greathouse IV, Apr 28 2010
a(6) = 4347 from Eric W. Weisstein, Jul 14 2013
a(7) = 37735 from Eric W. Weisstein, Jul 15 2013
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STATUS
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approved
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