为随机森林回归模型设置ntree和mtry的值

I'm using R package of random forest to do regression on some biological data and my training data size is 38772 X 201 and I just wonder what would be a good values for the number of trees "ntree" and the number of variable per level "mtry" and if there is an approximate formula to find such parameter values. each row in my input data is a 200 character representing the amino acid sequence and I want to build a regression model to use such sequence in order to predict the distances between the proteins. I'm using R package of random forest to do regr