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A091641
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Number of primes less than 10^n which do not contain the digit 7.
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10
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3, 16, 100, 680, 4773, 34992, 266823, 2079512, 16503238, 132852644, 1081509855, 8885472675, 73563855306, 612982476612
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OFFSET
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1,1
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COMMENTS
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Number of primes less than 10^n after removing any primes with at least one digit 7.
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LINKS
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FORMULA
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EXAMPLE
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a(2) = 16 because of the 25 primes less than 10^2, 9 have at least one digit 7; 25-9=16.
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MATHEMATICA
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NextPrim[n_] := Block[{k = n + 1}, While[ !PrimeQ[k], k++ ]; k]; c = 0; p = 1; Do[ While[ p = NextPrim[p]; p < 10^n, If[ Position[ IntegerDigits[p], 7] == {}, c++ ]]; Print[c]; p--, {n, 1, 8}] (* Robert G. Wilson v, Feb 02 2004 *)
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PROG
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(Python)
from sympy import primerange
def a(n): return sum('7' not in str(p) for p in primerange(2, 10**n))
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CROSSREFS
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KEYWORD
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more,nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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