A number of square pendulum figures with equal edge length, in the order: from top to bottom, 1 in the first layer, 3 in the second layer, 6 in the third layer, and 4 in the fourth layer A number of square pendulum figures with equal edge length, in the order of top to bottom One in the first layer, three in the second layer, six in the third layer, ten in the fourth layer, and fifteen in the fifth layer. What is the number of cubes in the nth layer? We stipulate that "△" is a new operational symbol. We know that 5 △ 3 = 5 + 6 + 7; 6 △ 2 = 6 + 7, 2 △ 4 = 2 + 3 + 4 + 5, then 3 △ 5= What's after the equal sign? Write out the process and I will score!

A number of square pendulum figures with equal edge length, in the order: from top to bottom, 1 in the first layer, 3 in the second layer, 6 in the third layer, and 4 in the fourth layer A number of square pendulum figures with equal edge length, in the order of top to bottom One in the first layer, three in the second layer, six in the third layer, ten in the fourth layer, and fifteen in the fifth layer. What is the number of cubes in the nth layer? We stipulate that "△" is a new operational symbol. We know that 5 △ 3 = 5 + 6 + 7; 6 △ 2 = 6 + 7, 2 △ 4 = 2 + 3 + 4 + 5, then 3 △ 5= What's after the equal sign? Write out the process and I will score!

The number of cubes in the nth layer is n / 2 × (n + 1)
Supplement: X △ y is the sum of Y integers starting from X, 3 △ 5 = 3 + 4 + 5 + 6 + 7