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A110054 Numbers n such that the string 222n is the decimal expansion of a prime number. 2
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified April 15 01:12 EDT 2021. Contains 342971 sequences. (Running on oeis4.)