Make a Table

	1	2	3	4	5
1	1,1C1	1,2C2	1,3C3	1,4C4	1,5C5
2	2,1C6	2,2C7	2,3C8	2,4C9	2,5C10
3	3,1C11	3,2C12	3,3C13	3,4C14	3,5C15

686 chars

Sample code

function makeRows(rowCount, colCount) {
    let row = "<th></th>";
    for (let j = 1; j <= colCount; j++) 
        row += "<th>"+j+"</th>";
    let text = "<tr>"+row+"</tr>";
    for (let i = 1; i <= rowCount; i++) {
       row = "<th>"+i+"</th>";
       for (let j = 1; j <= colCount; j++) {
          let p = colCount*(i-1)+j;
          let s = "<span class=tip>C"+p+"</span>"
          row += "<td>"+i+","+j+s+"</td>";
       }
       text += "<tr>"+row+"</tr>";
    }
    let t = text.length+" chars";
    console.log("makeRows: "+rowCount+"x"+colCount+" "+t);
    tablo.innerHTML = text; out.innerText = t; 
}