A110054 Numbers k such that the string 222k 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
Examples
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.
Links
- Robert Israel, Table of n, a(n) for n = 1..10000
Programs
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Magma
[ n: n in [1..700] | IsPrime(Seqint(Intseq(n) cat [2, 2, 2])) ]; // Klaus Brockhaus, Feb 03 2011
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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
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Mathematica
Select[Range[1000], PrimeQ[FromDigits[Join[{2, 2, 2}, IntegerDigits[ # ]]]] &] (* Alonso del Arte *) Select[Range[1000],PrimeQ[222*10^IntegerLength[#]+#]&] (* Harvey P. Dale, Oct 13 2024 *)
Extensions
More terms from Alonso del Arte, Sep 06 2005
Comments