A291605 Numbers k such that 5*10^k + 41 is prime.

2, 5, 8, 24, 35, 116, 208, 231, 237, 303, 1451, 1512, 2235, 2612, 4433, 4499, 5408, 7331, 11896, 12821, 23679, 23900, 59650, 122082, 151257, 159656

Offset

1,1

Comments

For k > 1, numbers k such that the digit 5 followed by k-2 occurrences of the digit 0 followed by the digits 41 is prime (see Example section).

a(27) > 2*10^5.

Links

Table of n, a(n) for n=1..26.

Makoto Kamada, Factorization of near-repdigit-related numbers.

Makoto Kamada, Search for 50w41.

Example

2 is in this sequence because 5*10^2 + 41 = 541 is prime.
Initial terms and associated primes:
a(1) = 2, 541;
a(2) = 5, 500041;
a(3) = 8, 500000041;
a(4) = 24, 5000000000000000000000041;
a(5) = 35, 500000000000000000000000000000000041; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[5*10^# + 41] &]

Prog

(PARI) isok(k) = ispseudoprime(5*10^k + 41); \\ Altug Alkan, Aug 27 2017

Crossrefs

Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.

Sequence in context: A195295 A088144 A100501 * A142869 A086825 A192476

Adjacent sequences: A291602 A291603 A291604 * A291606 A291607 A291608

Keyword

nonn,more,hard

Author

Robert Price, Aug 27 2017

Extensions

a(24)-a(26) from Robert Price, Mar 07 2019

Status

approved