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 A101395 Numbers n such that 4*10^n+7 is prime. 1
 0, 1, 3, 9, 39, 2323 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS No further terms < 50000. a(7) > 2*10^5. - Robert Price May 16 2015 LINKS Makoto Kamada, Prime numbers of the form 400...007. Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers. FORMULA a(n) = A101714(n-1) + 1. EXAMPLE n = 1, 3, 9 are members since 47, 4007 and 4000000007 are primes. MATHEMATICA Do[ If[ PrimeQ[4*10^n + 7], Print[n]], {n, 0, 10000}] PROG (PARI) is(n)=ispseudoprime(4*10^n+7) \\ Charles R Greathouse IV, Jun 12 2017 CROSSREFS Cf. A056806, A100501, A088274, A101714. Sequence in context: A090012 A079096 A143293 * A229244 A218504 A292909 Adjacent sequences:  A101392 A101393 A101394 * A101396 A101397 A101398 KEYWORD hard,nonn AUTHOR Julien Peter Benney (jpbenney(AT)ftml.net), Jan 15 2005 STATUS approved

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Last modified March 26 23:16 EDT 2019. Contains 321566 sequences. (Running on oeis4.)