2What is the formula for sodium bicarbonate?

I assume you mean you want the molecular formula for sodium bicarbonate - if you wanted a balanced equation, you would need another substance to react with

But sodium bicarbonate = NaHCO3

While the above answer is help full I am going to assume that the question was what is the balanced equation for the decomposition of sodium bicarbonate.

2NaHCO3--> Na2CO3+CO2+H2O

in further detail the reaction for this formula is not decomposition; it is, in fact, combustion because of the carbon dioxide and water in the products of the equation.