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 A047658 Numbers n such that the initial n digits in decimal portion of Pi form a prime number. 10
 5, 12, 281, 547, 6205, 16350 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Conjecture: this sequence is finite. - Carlos Rivera Rivera's conjecture that this sequence is finite conflicts with heuristics; the next entry is almost certainly 6205, since floor((Pi-3)*10^6205) is (very) probably prime, though its proof may take decades. - David Broadhurst, Nov 08 2000 Floor((Pi-3)*10^6205) is a strong pseudoprime to all (1229) prime bases a < 10000 (the test took 45 minutes). - Joerg Arndt, Jan 16 2011 Terms for n>=5 are only probable primes. - Dmitry Kamenetsky, Aug 03 2015 Floor((Pi-3)*10^16350) is a probable prime, checked with 25 iterations of the Miller-Rabin test. - Dmitry Kamenetsky, Aug 05 2015 The next term is greater than 65400. - Dmitry Kamenetsky, Aug 09 2015 LINKS C. K. Caldwell, Prime Curios: 14159...07021 (547-digits) EXAMPLE 5 gives 14159 (prime); 12 gives 141592653589 (prime) and so on. MATHEMATICA nn=1000; d=RealDigits[Pi-3, 10, nn][[1]]; Select[Range[nn], PrimeQ[FromDigits[Take[d, #]]] &] PROG (PARI) is(n)=isprime((Pi-3)*10^n\1) \\ Charles R Greathouse IV, Aug 28 2015 CROSSREFS Cf. A060421, A064118. Sequence in context: A096314 A323565 A195538 * A290804 A146542 A264873 Adjacent sequences:  A047655 A047656 A047657 * A047659 A047660 A047661 KEYWORD hard,nice,nonn,base,more AUTHOR STATUS approved

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Last modified October 18 02:23 EDT 2019. Contains 328135 sequences. (Running on oeis4.)