cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A278470 Numbers k such that 10^k - 201 is prime.

Original entry on oeis.org

13, 20, 40, 43, 73, 85, 576, 1676, 33565
Offset: 1

Views

Author

Vincenzo Librandi, Nov 23 2016

Keywords

Comments

For k > 2, numbers k such that k-3 occurrences of the digit 9 followed by the digits 799 is prime.
a(9) > 10000. - Robert G. Wilson v, Nov 24 2016

Examples

			13 is in this sequence because 10^13 - 201 = 9999999999799 is prime.
Initial terms and associated primes:
a(1) = 13, 9999999999799;
a(2) = 20, 99999999999999999799;
a(3) = 40, 9999999999999999999999999999999999999799; etc.

Links

Crossrefs

Cf. A108327 (10^n-21), this sequence (10^n-201), A278397 (10^n-20001), A278471 (10^n-2001).

Programs

  • Magma
    [n: n in [3..500] | IsPrime(10^n-201)];
  • Maple
    A278470:=n->`if`(isprime(10^n-201), n, NULL): seq(A278470(n), n=1..10^3); # Wesley Ivan Hurt, Dec 08 2016
  • Mathematica
    Select[Range[3, 2000], PrimeQ[10^# - 201] &]
  • PARI
    is(n)=ispseudoprime(10^n-201) \\ Charles R Greathouse IV, Jun 06 2017

Extensions

a(9) from Kamada data by Tyler Busby, May 03 2024
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