Primes on a Clock
Leave 6 adjacent numbers of the face of a clock intact and
rearrange the other 6 in such a way that the sum of every
pair of adjacent numbers is prime.
Leave as many numbers as possible in their correct positions
on the face of a clock and rearrange the rest such that the
sum of every pair of adjacent numbers is prime.
Repeat the previous problem, such that the sum of every adjacent pair
is composite (not prime).
Source: A small book called Problematical Recreations shown
to me by Bill Cleveland.
Used as Ken's POTD 3/7/94.
Mail to Ken