Re:The Pursuit of Beauty: Yitang Zhang solves a pure-math my...
by dragonwriter on Friday February 13, 2015 @08:50PM
(#9048385)
> However if you remove the 7, then the number is divisible by 2, so the statement: "A prime from which you can remove numbers and still have a prime is a deletable prime" does not apply to 1987.
A deletable prime doesn't require that the deletion order start from the last digit; the deletion order for 1987 is:
1987 -> 197 -> either 19 or 17
Re:The Pursuit of Beauty: Yitang Zhang solves a pure-math my...
by a3_nm on Friday February 13, 2015 @08:29PM
(#9048325)
The definition given in the article is an informal shortcut, the complete definition is http://mathworld.wolfram.com/DeletablePrime.html and 1987 is indeed a deletable prime (see http://oeis.org/A080608/b080608.txt for http://oeis.org/A080608).
"A prime from which you can remove numbers and still have a prime is a deletable prime, such as 1987".
However if you remove the 7, then the number is divisible by 2, so the statement: "A prime from which you can remove numbers and still have a prime is a deletable prime" does not apply to 1987.