How to write ARIMA model as formula

Hi guys!

I have a ARIMA model that looks like this:

> txc
Series: training[, 1] 
Regression with ARIMA(2,1,1)(0,0,1)[12] errors 

Coefficients:
          ar1      ar2     ma1    sma1       xreg
      -1.3060  -0.7919  0.8538  0.6626  -3083.430
s.e.   0.0972   0.1023  0.0890  0.1893    716.388

sigma^2 estimated as 567746:  log likelihood=-604.98
AIC=1221.96   AICc=1223.2   BIC=1235.87

But how can i see it as a formula?

Thanks in advance