The first number is 7, the second number is 19, the third number is 37, what's the nth number?

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