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A210720
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Primes formed by concatenating n, n, n, n, and 1 for n = 1, 2, 3,....
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2
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33331, 99991, 242424241, 404040401, 454545451, 464646461, 494949491, 525252521, 575757571, 737373731, 787878781, 949494941, 1021021021021, 1081081081081, 1091091091091, 1211211211211, 1291291291291, 1481481481481, 1511511511511
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OFFSET
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1,1
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COMMENTS
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This is to four (duplicated strings concatenated) as A210712 is to three (duplicated strings concatenated, and as A210511 is to two (duplicated strings concatenated).
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LINKS
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EXAMPLE
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a(1) = 33331 because Concat(3,3,3,1) = 3331 which is in A000040.
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MAPLE
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local p;
[n, n, n, n, 1] ;
p := digcatL(%) ;
if isprime(p) then
printf("%d, ", p) ;
end if;
end proc:
for n from 1 to 400 do
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MATHEMATICA
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Select[Table[FromDigits[Flatten[{IntegerDigits[n], IntegerDigits[n], IntegerDigits[n], IntegerDigits[n], IntegerDigits[1], {}}]], {n, 200}], PrimeQ] (* Vincenzo Librandi, Mar 15 2013 *)
Select[Table[FromDigits[Join[Flatten[IntegerDigits/@PadRight[{}, 4, n]], {1}]], {n, 200}], PrimeQ] (* Harvey P. Dale, Oct 16 2017 *)
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PROG
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(Magma) [nnnn1: n in [1..200] | IsPrime(nnnn1) where nnnn1 is Seqint([1] cat Intseq(n) cat Intseq(n) cat Intseq(n) cat Intseq(n))]; // Vincenzo Librandi, Mar 15 2013
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CROSSREFS
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KEYWORD
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nonn,base,easy
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AUTHOR
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STATUS
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approved
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