Question 548588
Did you skip a 9 in there? As written it is not a sequence/series that you would expect. It's like finding that the correct answer to "miss America" in a Jeopardy game is "If the USSR sent an intercontinental ballistic missile aimed at the US, what would you hope it would do?"
I would expect 1, 3, 5, 7, 9, 11, 13, ..., which I would call an arithmetic sequence (not a series), and it includes that 9, between the 7 and the 11. That would make it an arithmetic sequence with a common difference of 2 (where each number is the previous one plus 2).
I would describe it with the recursive formula {{{a[n]=a[n-1]+2}}} with {{{a[1]=1}}}
I could also use an explicit formula, such as
{{{a[n]=1+2(n-1)}}} or {{{a[n]=2n-1}}}