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Template:Sequence of the Day for February 17

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Intended for: February 17, 2012

Timetable

  • First draft entered by Alonso del Arte on November 13, 2011 based on a remark from Farideh Firoozbakht ✓
  • Draft reviewed by Daniel Forgues on February 16, 2016
  • Draft to be approved by January 17, 2012

Yesterday's SOTD * Tomorrow's SOTD

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A005936: Pseudoprimes to base 5.

{ 4, 124, 217, 561, 781, 1541, 1729, ... }
If both numbers
q
and
2 q  −  1
are primes, then
n = q  (2 q  −  1)
is a pseudoprime to base 5 if and only if
q
is of the form
10 k  +  1
.