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A322985
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Numbers k such that 123456789*10^k+1 is prime.
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0
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1, 5, 17, 23, 25, 28, 91, 187, 287, 398, 899, 1364, 2921, 5125, 5890, 8780, 14881, 35689, 46669, 71861, 111710
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OFFSET
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1,2
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COMMENTS
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a(22) > 1.3*10^5. All numbers up to this bound were sieved using newpgen and sr1sieve. Remaining numbers were checked for primality using Jean Penné's LLR application (BLS (N-1/N+1) test).
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LINKS
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EXAMPLE
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1 is a term because 1234567891 is prime.
2 is not a term because 12345678901 is composite (it is divisible by 857).
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MATHEMATICA
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PROG
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(Python)
from sympy.ntheory.primetest import isprime
for n in range(1, 1000):
if isprime(123456789*10**n+1):
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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STATUS
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approved
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