I got some users' history data and generated some sequences of real numbers. The length of each sequence is between 15 and 25. What's more, I do not know whether these sequences have patterns and the frequency is not known as well.

My goal is using each sequence to predict its next value, and then I use auto.arima in R to do this. However, the accuracy of the prediction is low.

Anyone have any good ideas to improve the accuracy?

One of these sequences is:

        1.5959709882736206  
        0.7300914525985718  
        2.0011744499206543  
        3.6755871772766113  
        0.8066112399101257  
        1.3413848876953125  
        3.371157646179199  
        0.4400146007537842  
        2.637667655944824  
        2.1453769207000732  
        2.341433048248291  
        2.3429665565490723  
        1.1187453269958496  
        1.4169363975524902  
        3.328829050064087  
        4.157748699188232  
        3.9255290031433105  
        2.7843635082244873