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Template:Sequence of the Day for September 5

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Intended for: September 5, 2011

Timetable

  • First draft entered by Alonso del Arte on May 31, 2011
  • Draft reviewed by Alonso del Arte on July 5, 2011
  • Draft to be approved by August 5, 2011
Yesterday's SOTD * Tomorrow's SOTD

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A059396: Number of primes less than
2  pn
, where
pn
is the
n
th prime.
{ 0, 0, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, ... }
This is the number of trial divisions by smaller primes to show that the
n
th prime is indeed prime. For example,
a (32) = 5
since the 32 nd prime is 131 which is not divisible by 2, 3, 5, 7 or 11 (and does not need to be tested against 13, 17, 19 etc. since 13 2 = 169 > 131).