Coin change, Reach a given score DP

def count(n):
    dp={}
    arr=[3,5,10]
    def help(coins,val):
        if val==0:return 1
        if coins<0 or val<0:return 0
        if (coins,val) in dp:return dp[(coins,val)]
        ans=0
        ans+=help(coins,val-arr[coins])+help(coins-1,val)
        dp[(coins,val)]=ans
        return ans
    return help(2,n)