A110054 Numbers n such that the string 222n is the decimal expansion of a prime number.

1, 29, 47, 59, 71, 73, 77, 79, 83, 91, 107, 109, 113, 127, 137, 149, 151, 161, 163, 193, 197, 199, 247, 269, 289, 293, 311, 317, 323, 329, 337, 347, 349, 361, 367, 379, 389, 403, 419, 437, 461, 493, 499, 511, 527, 533, 553, 557, 587, 601, 613, 619, 643, 647

Offset

1,2

Comments

All terms == 1 or 5 (mod 6). - Robert Israel, Oct 30 2019

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

1 is in the sequence because 2221 is prime.
91 is in the sequence because 22291 is prime.
109 is in the sequence because 222109 is prime.

Maple

select(t -> isprime(222*10^(1+ilog10(t))+t), [seq(seq(6*i+j, j=[1, 5]), i=0..1000)]); # Robert Israel, Oct 30 2019

Mathematica

Select[Range[1000], PrimeQ[FromDigits[Join[{2, 2, 2}, IntegerDigits[ # ]]]] &] (* Alonso Delarte *)

Prog

(Magma) [ n: n in [1..700] | IsPrime(Seqint(Intseq(n) cat [2, 2, 2])) ]; // Klaus Brockhaus, Feb 03 2011

Crossrefs

Sequence in context: A248429 A077782 A059414 * A104912 A104913 A225303

Adjacent sequences: A110051 A110052 A110053 * A110055 A110056 A110057

Keyword

nonn,base

Author

Parthasarathy Nambi, Sep 04 2005

Extensions

More terms from Alonso del Arte, Sep 06 2005

Status

approved