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