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A281252
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Numbers whose septenary, octal and nonary representations are prime when read in decimal.
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1
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2, 3, 5, 43, 115, 619, 1249, 1681, 1711, 2563, 2635, 5155, 10321, 10531, 11539, 13219, 14479, 17713, 17755, 18217, 18889, 20203, 20905, 26335, 27163, 29305, 35353, 39859, 40867, 40897, 40993, 44425, 44803, 51145, 52993, 55735, 57751, 58075, 68335, 68839, 69553
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OFFSET
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1,1
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COMMENTS
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After a(1) all the terms are odd.
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LINKS
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EXAMPLE
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a(6) = 619 is in the sequence because 619_10 = 1543_7 = 1153_8 = 757_9; and 1543, 1153 and 757 are prime when read in decimal.
a(7) = 1249 is in the sequence because 1249_10 = 3433_7 = 2341_8 = 1637_9; and 3433, 2341 and 1637 are prime when read in decimal.
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MATHEMATICA
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Select[Range[500000], PrimeQ[FromDigits[IntegerDigits[#, 7]]] && PrimeQ[FromDigits[IntegerDigits[#, 8]]] && PrimeQ[FromDigits[IntegerDigits[#, 9]]] &]
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PROG
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(PARI) is(n)=for(b=7, 9, if(!isprime(fromdigits(digits(n, b))), return(0))); 1 \\ Charles R Greathouse IV, Jan 22 2017
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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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