[Python 2], 104 94 89 bytes

s=n=input()
while s:print' '*(s+1)+'/ '*(n-s)+'_'*(2*s+len(`n`));s-=1
print'\/'*n+' '+`n`

[Try it online!][TIO-k9zf5o77]

Edit 1: Forgot I switched to python 2 lol

Edit 2: Thanks @ElPedro for the idea of switching to while loop! [Python 2]: https://docs.python.org/2/ [TIO-k9zf5o77]: https://tio.run/##JY1BCsIwEEX3c4rsJpNQaiLdKLmJYKEONFCmwYmop48p7h583vvlW9ddYlv2B5tkELFpkpSlvKoleK95Y6OX8sxS0aCz6gN5HA@UQTveO0WnfmOxs8xEVx1SgL9xG9GJ76LvU@t14A8v9nhzE7UAEc4wQTj9AA "Python 2 – Try It Online"