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A275978
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Numbers k such that (101*10^k + 1)/3 is prime.
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0
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1, 4, 6, 12, 34, 54, 60, 61, 73, 148, 349, 552, 649, 967, 1044, 2521, 4501, 5721, 6133, 9052, 9880, 16126, 16215, 19146, 61770
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OFFSET
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1,2
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COMMENTS
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Numbers k such that the digits 33 followed by k-1 occurrences of the digit 6 followed by the digit 7 is prime (see Example section).
a(26) > 10^5.
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LINKS
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EXAMPLE
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4 is in this sequence because (101*10^4 + 1)/3 = 336667 is prime.
Initial terms and associated primes:
a(1) = 1, 337;
a(2) = 4, 336667;
a(3) = 6, 33666667;
a(4) = 12, 33666666666667;
a(5) = 34, 336666666666666666666666666666666667, etc.
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MATHEMATICA
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Select[Range[0, 100000], PrimeQ[(101*10^# + 1)/3] &]
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PROG
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(PARI) isok(n) = isprime((101*10^n + 1)/3); \\ Michel Marcus, Aug 16 2016
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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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