@types/bn.js must be installed to import this library

[remagpie]

When I try to import this library in typescript, I get the following error:

error TS7016: Could not find a declaration file for module 'bn.js'. '.../node_modules/bn.js/lib/bn.js' implicitly has an 'any' type.
  Try `npm install @types/bn.js` if it exists or add a new declaration (.d.ts) file containing `declare module 'bn.js';`

1 import BN = require("bn.js");