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A123933
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a(n) = smallest positive composite integer such that a(n)-10^k is prime for all k=1,2..n.
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0
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OFFSET
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1,1
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COMMENTS
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a(n)=0 (mod 7) for n>6.
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LINKS
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EXAMPLE
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a(3)=1007 is included as 997, 907 and 7 are primes.
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PROG
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(PARI) a(n) = {m = 10^n; ok = 0; while (! ok, if (! isprime(m), ok = 1; for (k=1, n, if (! isprime(m-10^k), ok = 0; break; ); ); ); if (! ok, m++); ); return (m); } \\ Michel Marcus, Jul 16 2013
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CROSSREFS
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KEYWORD
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hard,nonn
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AUTHOR
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Anton Vrba (antonvrba(AT)yahoo.com), Nov 29 2006
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EXTENSIONS
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STATUS
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approved
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