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A280576
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Primes formed from the concatenation of previousprime(n) and n.
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1
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23, 79, 3137, 3739, 4751, 6163, 8387, 8389, 109111, 113117, 113123, 151153, 151157, 157163, 167173, 173177, 181183, 199207, 199211, 211213, 211217, 211219, 233239, 241249, 251257, 257263, 263267, 263269, 271273, 271277, 277279, 283289, 317321, 317323, 317327
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OFFSET
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1,1
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LINKS
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EXAMPLE
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79 is in the sequence because it is a prime formed from the concatenation of 7 and 9, where 7 is the largest prime < 9.
8387 is in the sequence because it is a prime formed from the concatenation of 83 and 87, where 83 is the largest prime < 87.
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MATHEMATICA
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Select[Table[FromDigits[Join[IntegerDigits[Prime[PrimePi[n - 1]]], IntegerDigits[n]]], {n, 3, 1000}], PrimeQ]
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PROG
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(Magma) [p : n in[3..200] | IsPrime (p) where p is Seqint (Intseq (n) cat Intseq (PreviousPrime (n)))];
(PARI) terms(n) = my(i=0, x=3); while(1, my(cc=eval(Str(precprime(x-1), x))); if(ispseudoprime(cc), print1(cc, ", "); i++); if(i==n, break); x++)
/* Print initial 40 terms as follows: */
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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