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 A153450 Number of primes <= 2^(2^n) = pi(A001146(n)). 0
 1, 2, 6, 54, 6542, 203280221, 425656284035217743 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS The primes up to 2^(2^n) are exactly determined from the primes up to 2^(2^(n-1)), n >= 1, with the sieve of Eratosthenes. This gives an inductive algorithm to find all primes up to any integer (modulo space and time constraints...) This means that all odd primes are ultimately determined by the even prime, 2. - Daniel Forgues, Dec 04 2011 LINKS H. J. Smith, XICalc - Extra Precision Integer Calculator. FORMULA a(n) = pi(2^(2^n)) = A007053(2^n). EXAMPLE a(3) = 54 because 2^(2^3) = 256 and there are 54 primes <= 256. PROG (Other) (XICalc) Pi(2^(2^n)); (PARI) a(n)=primepi(1<<2^n) \\ Charles R Greathouse IV, Dec 05 2011 CROSSREFS Cf. A001146. Sequence in context: A122593 A267348 A264610 * A179389 A084123 A193473 Adjacent sequences:  A153447 A153448 A153449 * A153451 A153452 A153453 KEYWORD nonn AUTHOR Harry J. Smith, Dec 27 2008 EXTENSIONS a(6) from Charles R Greathouse IV, Dec 05 2011 STATUS approved

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Last modified May 17 22:15 EDT 2021. Contains 343992 sequences. (Running on oeis4.)