A290956 - OEIS

A290956

Numbers k such that (13*10^k + 191)/3 is prime.

1, 3, 4, 18, 28, 40, 45, 49, 78, 165, 312, 469, 855, 899, 1137, 1314, 1410, 3832, 10518, 24163, 28792, 36947, 56909, 58103, 59797, 139782

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OFFSET

1,2

COMMENTS

For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 3 followed by the digits 97 is prime (see Example section).

a(27) > 2*10^5.

LINKS

EXAMPLE

3 is in this sequence because (13*10^3 + 191)/3 = 4397 is prime.

Initial terms and associated primes:

a(1) = 1, 107;

a(2) = 3, 4397;

a(3) = 4, 43397;

a(4) = 18; 4333333333333333397;

a(5) = 28, 43333333333333333333333333397; etc.

MATHEMATICA

Select[Range[0, 100000], PrimeQ[(13*10^# + 191)/3] &]

CROSSREFS

KEYWORD

nonn,more,hard

AUTHOR

Robert Price, Aug 14 2017

EXTENSIONS

a(26) from Robert Price, Nov 28 2018

STATUS

approved