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A319858
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a(n) is the number of values of m in the interval [2,10] such that the base-m expansion of n, interpreted as a base-10 number, yields a prime.
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0
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0, 8, 8, 1, 7, 1, 5, 2, 2, 3, 3, 1, 3, 0, 2, 2, 3, 0, 4, 0, 2, 2, 4, 0, 2, 1, 1, 2, 3, 0, 3, 0, 3, 2, 1, 0, 4, 1, 3, 0, 2, 0, 5, 0, 1, 1, 3, 1, 1, 1, 0, 1, 2, 0, 4, 1, 1, 1, 3, 0, 3, 0, 1, 1, 1, 1, 4, 1, 0, 0, 5, 0, 2, 0, 2, 0, 1, 0, 4, 0, 1, 1, 3, 1, 1, 0, 2, 1, 3, 0, 2, 0, 2, 2, 1, 0, 3, 0, 0, 0
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OFFSET
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1,2
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LINKS
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EXAMPLE
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a(31)=3 because 31 yields primes for 3 bases in [2,10]: 31 = 11111_2 = 1011_3 = 133_4 = 111_5 = 51_6 = 43_7 = 37_8 = 34_9 = 31_10, and of the decimal numbers 11111, 1011, 133, 111, 51, 43, 37, 34, and 31, the 3 primes are 43, 37, and 31.
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MATHEMATICA
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Array[Count[FromDigits /@ IntegerDigits[#, Range[2, 10]], _?PrimeQ] &, 105] (* Michael De Vlieger, Oct 11 2018 *)
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PROG
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(PARI) a(n) = sum(b=2, 10, isprime(fromdigits(digits(n, b), 10))); \\ Michel Marcus, Sep 30 2018
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CROSSREFS
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KEYWORD
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nonn,base,easy
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AUTHOR
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STATUS
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approved
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