In the world of numbers, numbers 1 to 9 want to cross a river,
They have a boat which can take 1 to 3 numbers,
But sum of the numbers must be a square number.
The boat can not sail back itself, so there must be some numbers to sail back.
Plan minimum number of trips in such a way that all the numbers can cross the river.
I use Microsoft Clip art organizer to search the individual pictures (boat and man) then compose the picture.