A275524 Numbers n such that (56*10^n + 223)/9 is prime.

0, 2, 3, 5, 8, 32, 36, 53, 92, 126, 156, 158, 536, 639, 846, 1356, 1953, 2237, 4407, 5082, 17447, 17922, 24806, 25926, 29699, 30474, 37424, 63942

Offset

1,2

Comments

For n>1, numbers such that the digit 6 followed by n-2 occurrences of the digit 2 followed by the digits 47 is prime (see Example section).

a(29) > 10^5.

Links

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

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

Makoto Kamada, Search for 62w47.

Example

3 is in this sequence because (56*10^3 + 223)/9 = 6247 is prime.
Initial terms and primes associated:
a(1) = 0, 31;
a(2) = 2, 647;
a(3) = 3, 6247;
a(4) = 5, 622247;
a(5) = 8, 622222247, etc.

Mathematica

Select[Range[0, 100000], PrimeQ[(56*10^# + 223)/9] &]

Prog

(Magma) [n: n in [0..500] | IsPrime((56*10^n+223) div 9)]; // Vincenzo Librandi, Aug 01 2016
(PARI) is(n)=ispseudoprime((56*10^n+223)/9) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

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

Sequence in context: A273003 A014258 A237575 * A177195 A178355 A281618

Adjacent sequences: A275521 A275522 A275523 * A275525 A275526 A275527

Keyword

nonn,more

Author

Robert Price, Jul 31 2016

Status

approved