why is a text not displayed?

I made this along a tutorial.

However 

"Hello, world. You're at the blog index."

is not displayed.

"""blog/views.py"""
from django.http import HttpResponse


def index(request):
    return HttpResponse("Hello, world. You're at the blog index.")
"""blog/urls"""
from django.urls import include, path
from django.contrib import admin
from . import views

urlpatterns = [
    path('', views.index, name='index'),
    path('blog/', include('blog.urls')),
    path('admin/', admin.site.urls),
]

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