Op amp input biasing
Just to tidy things up - (the answer has been given by Peter,Mkeith and Spehro et al.)



R1 and R2 form a voltage divider - as they are equal this means that half the supply voltage is at their mid point. R3 connects this voltage to the non inverting input (less a negligible drop for input bias).

C1 allows only AC input to the non inverting input which is offset by the 1/2 V.

The op amp is configured as a non inverting amp. The gain is determined by R4,C2 and R5. For mid range gain the impedance of the capacitor is negligible so the AC gain is 1 + R5/R4  = 21.

Looking at the DC gain the capacitors are effectively open circuits. The configuration is now a unity voltage follower. The only input is the 1/2V from the voltage divider (R1,R2). The output will be 1/2 V. The value of R5 doesn't come into the calculation and could be replaced with a wire link.

What the circuit will do is to give a DC output of 1/2V and add to that an AC signal 21 times the input AC input signal.