Sample to display GeoJSON as cluster in Openlayers 3. derived from http://openlayers.org/en/v3.6.0/examples/cluster.html?mode=advanced

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Clustering example</title>
<script src="https://code.jquery.com/jquery-1.11.2.min.js"></script>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/css/bootstrap.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/ol3/3.6.0/ol.css" type="text/css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/ol3/3.6.0/ol.js"></script>
</head>
<body>
<div class="container-fluid">

</div>
<script>

var source = new ol.source.Vector({
    url: 'sample.geojson',
    format: new ol.format.GeoJSON()
});

var clusterSource = new ol.source.Cluster({
  distance: 40,
  source: source
});

var raster = new ol.layer.Tile({
  source: new ol.source.MapQuest({layer: 'sat'})
});

var raw = new ol.layer.Vector({
  source: source
});

var map = new ol.Map({
  layers: [raster, clusters],
  renderer: 'canvas',
  target: 'map',
  view: new ol.View({
    center: [0, 0],
    zoom: 2
  })
});

</script>
</body>
</html>

https://code.jquery.com/jquery-1.11.2.min.js

https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/js/bootstrap.min.js

https://cdnjs.cloudflare.com/ajax/libs/ol3/3.6.0/ol.js