Template:Sequence of the Day for September 5

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).