Re: [math-fun] sum-product matrices

I'm pretty sure that apart from 1 x 1 matrices, there are no square sum-product matrices.

1 10 15 12 6 8 20 4 2

But I was pleased to find that there are indeed sum-product matrices with equal row sum and column product. The following are (all?) "primitive" 14 x 2 sum-product matrices with sum = product = 1890.

there is a 10x2 sum-product matrix with equal row sum 840 and column product 840: 2 4 7 24 40 70 105 140 168 280 420 210 120 35 21 12 8 6 5 3 you can find more info on sum-product matrices here: http://www2.stetson.edu/~efriedma/mathmagic/1102.html erich