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 A091641 Number of primes less than 10^n which do not contain the digit 7. 10
 3, 16, 100, 680, 4773, 34992, 266823, 2079512, 16503238, 132852644, 1081509855, 8885472675, 73563855306, 612982476612 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Number of primes less than 10^n after removing any primes with at least one digit 7. LINKS FORMULA a(n) = A006880(n) - A091708(n). EXAMPLE a(2) = 16 because of the 25 primes less than 10^2, 9 have at least one digit 7; 25-9=16. MATHEMATICA 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 *) PROG (Python) from sympy import primerange def a(n): return sum('7' not in str(p) for p in primerange(2, 10**n)) print([a(n) for n in range(1, 7)]) # Michael S. Branicky, Mar 16 2021 CROSSREFS Cf. A091634, A091635, A091636, A091637, A091638, A091639, A091640, A091642, A091643. Sequence in context: A303831 A193037 A246056 * A137572 A009151 A009007 Adjacent sequences:  A091638 A091639 A091640 * A091642 A091643 A091644 KEYWORD more,nonn,base AUTHOR Enoch Haga, Jan 30 2004 EXTENSIONS Edited and extended by Robert G. Wilson v, Feb 02 2004 a(9)-a(12) from Donovan Johnson, Feb 14 2008 a(13) from Robert Price, Nov 08 2013 a(14) from Giovanni Resta, Mar 20 2017 STATUS approved

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Last modified May 11 03:49 EDT 2021. Contains 343784 sequences. (Running on oeis4.)