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A273097
Numbers k such that 4*10^k + 87 is prime.
0
1, 2, 4, 5, 13, 25, 27, 32, 37, 38, 40, 45, 57, 80, 91, 151, 214, 441, 644, 764, 797, 1222, 2329, 2931, 4324, 21794, 22396, 24041, 46420, 51489, 55165, 126625
OFFSET
1,2
COMMENTS
For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 0 followed by the digits 87 is prime (see Example section).
a(33) > 3*10^5.
EXAMPLE
4 is in this sequence because 4*10^4 + 87 = 40087 is prime.
Initial terms and associated primes:
a(1) = 1, 127:
a(2) = 2, 487;
a(3) = 4, 40087;
a(4) = 5, 400087;
a(5) = 13, 40000000000087, etc.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[4*10^# + 87] &]
PROG
(PARI) is(n)=ispseudoprime(4*10^n + 87) \\ Charles R Greathouse IV, Jun 13 2017
KEYWORD
nonn,more
AUTHOR
Robert Price, May 15 2016
EXTENSIONS
a(32) from Robert Price, Aug 15 2018
STATUS
approved