Q: known arithmetic sequence: 1,5,9,13,17,21. Find the sum of the first 360 terms

360+360*359*2=258660

In the arithmetic sequence 1.5.9.13.17 ', what is 401?

an=4n-3
When an = 401
4n-3=401
n=101
Item 101

Arithmetic sequence 5,9,13,17 What is 401?

The first number is 5,
The second number 9 = 5 + (2-1) * 4
The third number 13 = 5 + (3-1) * 4
The fourth number 17 = 5 + (4-1) * 4
……
401=5+（100-1）*4
That is to say, 401 is item 100

Find the rule, 1,5,9,13,17... The representation of the nth number?

4n-3

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