user.js

router.get('/:page', (req, res) => {
  let page = req.params.page;      // page number
  let limit = 50;   // number of records per page
  let offset = page * limit;
  	
  db.user.findAndCountAll({
      attributes: ['id', 'first_name', 'last_name', 'date_of_birth'],
      limit: limit,
      offset: offset,
      $sort: { id: 1 }
  }).then((data) => {
    let pages = Math.ceil(data.count / limit);
		offset = limit * (page - 1);
    let users = data.rows;
    res.status(200).json({'result': users, 'count': data.count, 'pages': pages});
 })
  .catch(function (error) {
	res.status(500).send('Internal Server Error');
   });
});

Why do you set offset in line 13 again? Shouldn't it be "limit * (page - 1)" in line 4?