Random & Unique CSS Gradient-Color Generator

// HTML CODE
// <h1>Welcome to the game!</h1>
//   <input type="text" name="number" id="" onkeyup="generate(this)"
//      placeholder="Enter your favourite number and then press TAB">
// <div id="result">

let generate = (ele) => {
    if (!isNaN(ele.value)) {
        document.getElementById("result").innerHTML = "";
        // alert(ele.value);
        let letters = "0123456789ABCDEF";
        array_1 = [];
        array_2 = [];
        for (i = 0; i < ele.value; i++) {
            let color_1 = '#';
            let color_2 = '#';
            do {
                for (let i = 0; i < 6; i++) {
                    color_1 += letters[(Math.floor(Math.random() * 16))];
                    color_2 += letters[(Math.floor(Math.random() * 16))];
                }
                array_1.push(color_1);
                array_2.push(color_2);
            } while (!array_1.includes(color_1) && array_2.includes(color_2));
            let div = document.createElement("div");
            div.style.width = "200px";
            div.style.height = "200px";
            div.style.backgroundImage = "linear-gradient(to right," + color_1 + "," + color_2 + ")";
            div.style.color = "white";
            div.style.display = "inline-flex";
            div.style.margin = "25px";
            document.getElementById("result").appendChild(div);
        }
        array_1 = [];
        array_2 = [];
    } else {
        alert("Only Number is allowed");
        document.getElementById("result").innerHTML = "";
    }
}