The Pyramid of Numbers

                                1 = 1                 = 1²

                            1+2+1 = 2+2               = 2²

                        1+2+3+2+1 = 3+3+3             = 3²

                    1+2+3+4+3+2+1 = 4+4+4+4           = 4²

                1+2+3+4+5+4+3+2+1 = 5+5+5+5+5         = 5²

            1+2+3+4+5+6+5+4+3+2+1 = 6+6+6+6+6+6       = 6²

        1+2+3+4+5+6+7+6+5+4+3+2+1 = 7+7+7+7+7+7+7     = 7²

    1+2+3+4+5+6+7+8+7+6+5+4+3+2+1 = 8+8+8+8+8+8+8+8   = 8²

1+2+3+4+5+6+7+8+9+8+7+6+5+4+3+2+1 = 9+9+9+9+9+9+9+9+9 = 9²