input:1 output:4

input:2 output:7
input:3 output:10
input:4 output:13

What is the rule?

3 answers

the rule is x3+1
Looks more like 3x+1

technically, since multiplication is commutative, x3 is the same as 3x, but you will find most people put the numeric coefficient first. . .
53
16564
21641
60
3
140.

2548