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 A071620 Integer lengths of the Champernowne primes (concatenation of first a(n) entries (digits) of A033307 is prime). 5
 10, 14, 24, 235, 2804, 4347, 37735 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 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 LINKS 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 MATHEMATICA 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 *) PROG (Python) from itertools import count, islice from sympy import isprime def A071620_gen(): # generator of terms c, l = 0, 0 for n in count(1): for d in str(n): c = 10*c+int(d) l += 1 if isprime(c): yield l A071620_list = list(islice(A071620_gen(), 5)) # Chai Wah Wu, Feb 27 2023 CROSSREFS 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 KEYWORD nonn,base,hard,more AUTHOR Robert G. Wilson v, Jun 21 2002 EXTENSIONS 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 STATUS approved

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Last modified May 18 02:52 EDT 2024. Contains 372617 sequences. (Running on oeis4.)