The first number is 7, the second number is 19, the third number is 37, what's the nth number?
Is it 7 + ((n-1) * (n + 2) * 6) / 2
The second number is 19 = 7 + 12 = 7 + 2 * 6
The third number is 37 = 19 + 18 = 19 + 3 * 6
It can be seen that the n-1st number of the nth number plus N * 6, and then we can get n = 7 + ((n-1) * (n + 2) * 6) / 2
I have to hand in my homework tomorrow. Find the sum formula of 1 / 2 + 3 / 4 +. + 99 / 100
I haven't seen it in a year. Forget it
Several, 1: (first term + last term) × number of terms △ 2, find the number of terms: (last term - first term) △ difference number + 1; the second: intermediate number (average, sum of first and last term △ 2) × number of terms