All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars
 perplexus dot info

 An Odd Couple (Posted on 2009-01-10)
There are 43 3-digit prime numbers which, when reversed, also yield a prime number. (Eight of these are actually consecutive primes).

Of the 43, 15 are simply palindromes (e.g. 929), but of the remaining 14 pairs of numbers (called 'emirp's), one pair in particular exhibits two unique characteristics, one of which is rather surprising.

What are the numbers, and what are their unique characteristics?

 See The Solution Submitted by rod hines No Rating

Comments: ( Back to comment list | You must be logged in to post comments.)
 here are the pairs | Comment 1 of 9
`list    5   dim P(150)   10   while N<1000   20   N=nxtprm(N)   30   if N>100 and N<1000 then   40     :S=cutspc(str(N))   50     :if left(S,1)<>right(S,1) then   60       :Ct=Ct+1:P(Ct)=cutspc(str(N))   70   wend   80   for I=1 to Ct-1   90   for J=I+1 to Ct  100   if left(P(I),1)=right(P(J),1) and left(P(J),1)=right(P(I),1) then  105    :if mid(P(I),2,1)=mid(P(J),2,1) then  110      :print P(I),P(J)  120   next  130   nextOKrun107     701113     311149     941157     751167     761179     971199     991337     733347     743359     953389     983709     907739     937769     967OK`

Now, what's special about one of these pairs?

 Posted by Charlie on 2009-01-10 14:23:33

 Search: Search body:
Forums (0)