ipywidgets are not working in .ipynb

from ipywidgets import interact
@interact
def calculate(x=2):
    print(x**2)

The output is an interactive object string , instead of the actual widget:
[Out] interactive(children=(IntSlider(value=2, description='x', max=6, min=-2), Output()), _dom_classes=('widget-int…

Am I missing something, or if someone know how to get it working?