Template:Sequence of the Day for February 17

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

The line below marks the end of the <noinclude> ... </noinclude> section.

---

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

.