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A057875
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Numbers of 2n-digit primes which are concatenations of n-digit primes (no leading zeros allowed).
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0
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OFFSET
| 1,1
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LINKS
| C. K. Caldwell, Prime Curios! 80
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EXAMPLE
| n=1 gives these four primes 23, 37, 53 and 73.
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PROG
| (PARI) for(n=1, 5, pdn=vector(10^n-10^(n-1)); i=1; for(k=10^(n-1)+1, 10^n-3, if(isprime(k), pdn[i]=k; i++)); s=0; for(l=1, i-1, for(m=1, i-1, if(isprime(pdn[l]*(10^n)+pdn[m]), s++))); print1(s", ")) - Herman Jamke (hermanjamke(AT)fastmail.fm), Mar 30 2008
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CROSSREFS
| Cf. A000040.
Sequence in context: A132584 A012127 A189791 * A187543 A012824 A012057
Adjacent sequences: A057872 A057873 A057874 * A057876 A057877 A057878
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KEYWORD
| nonn,base,more
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AUTHOR
| Patrick De Geest (pdg(AT)worldofnumbers.com), Sep 15 2000.
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EXTENSIONS
| a(5) from Herman Jamke (hermanjamke(AT)fastmail.fm), Mar 30 2008
a(6)-a(7) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Dec 19 2010
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