A281644 Numbers k such that 2*10^k + 41 is prime.

0, 1, 2, 5, 11, 13, 14, 36, 37, 41, 43, 49, 53, 138, 146, 269, 313, 428, 517, 860, 1297, 3185, 4477, 6737, 14204, 68744, 170767, 184723

Offset

1,3

Comments

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

a(29) > 2*10^5.

Links

Table of n, a(n) for n=1..28.

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

Makoto Kamada, Search for 20w41.

Example

2 is in this sequence because 2*10^2 + 41 = 241 is prime.
Initial terms and associated primes:
a(1) = 0, 43;
a(2) = 1, 61;
a(3) = 2, 24;
a(4) = 5, 200041;
a(5) = 11, 200000000041; etc.

Mathematica

Select[Range[0, 100000], PrimeQ[2*10^# + 41 &]

Crossrefs

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

Sequence in context: A065433 A032541 A363981 * A075749 A138837 A038899

Adjacent sequences: A281641 A281642 A281643 * A281645 A281646 A281647

Keyword

nonn,more,hard

Author

Robert Price, Jan 25 2017

Extensions

a(27)-a(28) from Robert Price, May 05 2018

Status

approved