Question: The largest chess streamer on YouTube is GothamChess (Levy Rozman), who currently has over 4 million subscribers. The number of Gotham subscribers can be modeled by the arithmetic sequence an, where a, is the number of Gotham subscribers (in millions) for month n (n =1 represents January 2021).If Gotham Chess had 1.66 million subscribers in month 9

The largest chess streamer on YouTube is GothamChess $($Levy Rozman$),$ who currently has over $4$ million subscribers. The number of Gotham subscribers can be modeled by the arithmetic sequence an$,$ where a$,$ is the number of Gotham subscribers $($in millions$)$ for month n $($n $=1$ represents January $2021).$If Gotham Chess had $1\mathrm{.}66$ million subscribers in month $9$ and ant $-$ an $=0\mathrm{.}143$ for n$1,$ how many subscribers $($in millions$)$ does the arithmetic model predict GothamChess will have for month $13?$