A293592 - OEIS

A293592

Numbers k such that 3*10^k - 59 is prime.

2, 5, 7, 55, 70, 188, 248, 273, 385, 416, 479, 530, 574, 892, 1833, 4057, 4299, 6188, 14699, 21121, 88293, 89608, 95776, 162620, 196881

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OFFSET

1,1

COMMENTS

For k > 1, numbers k such that the digit 2 followed by k-2 occurrences of the digit 9 followed by the digits 41 is prime (see Example section).

a(26) > 2*10^5.

LINKS

EXAMPLE

2 is in this sequence because (3*10^2 - 59)/3 = 241 is prime.

Initial terms and associated primes:

a(1) = 2, 241;

a(2) = 5, 299941;

a(3) = 7, 29999941;

a(4) = 55, 29999999999999999999999999999999999999999999999999999941; etc.

MATHEMATICA

Select[Range[2, 100000], PrimeQ[(3*10^# - 59)/3] &]

CROSSREFS

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Oct 12 2017

EXTENSIONS

a(24)-a(25) from Robert Price, Sep 08 2018

STATUS

approved