Template:Sequence of the Day for February 18

Intended for: February 18, 2014

Timetable

• First draft entered by Alonso del Arte on February 18, 2013 ✓
• Draft to be reviewed by December 18, 2011
• Draft to be approved by January 18, 2012

Yesterday's SOTD * Tomorrow's SOTD

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A195264 Iterate x ↦ A080670 (x) starting at

n

until reaching 1 or a prime; or  − 1 if a noncomposite is never reached.

{ 1, 2, 3, 211, 5, 23, 7, 23, 2213, ... }

For example, 9 = 3 2 ↦ 32 = 2 5 ↦ 25 = 5 2 ↦ 52 = 2 2  ⋅  13 ↦ 2213, which is prime, so a (9) = 2213. It remains an open question whether the  − 1 is ever needed, with the smallest value, 20, having so far been tested past 70 iterations.