Cuando haces clic en el botón, la consola dice:
project3.html:48 Error de referencia no detectado: findnembers no está definido en HTMLButtonElement.onclick (project3.html:48)
¿Porqué es eso?
<html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>project3</title> </head> <body dir="ltr"> <button id="click here to calculate" onclick="findnembers();" type=button>click here to calculate </button> <div id='rslt' style='text-align: center;font-size: 1em; font-weight: bolder;' value=""></div> <script> function sumdigits(num) { sum = 0; while (num) { sum += num % 10; num = Math.floor(num / 10); } return sum; } function findnembers() { var counter = 0; var list='<ol>'; for (let i = 0; i < 9999; i++) { var ezer = sumdigits(i); if (ezer === 9) { list+= "<li>" + i + "</li>"; counter++; } list += "</ol>"; } var print=list+ <p style='text-align: center;font-size: 1em; font-weight: bolder;'>"The sum of digits of those number is 9, and they are in the range 0 to 9999 inclusive and their quantity is "{counter}</p>; document.getElementById("rslt").innerHTML=print; } </script> </body> </html>```como dijo @kinglish citando. debería ser así
var print=`${list}<p style='text-align: center;font-size: 1em; font-weight: bolder;'>"The sum of digits of those number is 9, and they are in the range 0 to 9999 inclusive and their quantity is "${counter}</p>`;