____ /\ \ ____/ \___\ /\ \ / / ____/ \ \/___/ /\ \ \ \ ____/ \ \ \_______\ /\ \ \ \ / / / \ \ \ \/_______/ \ \ \ \ \ \ \ \ \___________\ \ \ \ / / \ \ \/___________/ \ \ \ \ \_______________\ \ / / \/_______________/

the reference is: giorgio goldoni, a visual proof for the sum of the first n squares and for the sum of the first n factorials of order two, mathematical intelligencer, v. 24, no. 4 (2002) pp. 67-69. try this url: http://tinyurl.com/2vgsuo (it might require some proxy access, i'm not certain about that.) mike