O O O
 O O O
O O O

nearby pennies touching. By the fewest number of legal moves, transform the pattern into the pattern

   O
  O O
 O   O
O O O O

nearby pennies touching. A legal move consists of sliding a penny, not picking up a penny, without disturbing the other pennies, to a new position touching at least two pennies.

Right.  If it could be done in 3 moves, then six of the pennies must already be part of the finished triangle.  But then these 6 stationary pennies block the center penny from sliding.

"4 moves should be easy, though"?  Wasn't so easy for me.