The Numerical Recipes™ book, and its electronic subscription version Numerical Recipes Electronic, are sold as text and reference works, for reading and educational purposes. If you intend to use Numerical Recipes code on a computer, you need a separate license.

There are two kinds of licenses.

1. With the purchase of a Numerical Recipes Code product, either a code download or a Numerical Recipes Code CD-ROM, you automatically get a non-expiring Numerical Recipes Personal, Single-User License that allows one individual to use the code on any number of computers.

2. With the purchase of a Numerical Recipes institutional subscription, you get a Numerical Recipes Institutional Subscriber License that allows use of the code by any number of individuals on computers within a subscriber's fixed IP address range, during the term of the subscription.

See complete license terms for both license types here.

Bound "invisibly" into your executable .exe file? Generally yes. As source code, linkable object libraries, or DLLs? Generally no. See more details here.

Yes, if each such license purchased is permanently assigned to a specific individual before it is first used. Note, however, that the Personal, Single-User License may be assigned only once, to a single individual. Thereafter it stays with that individual, whether or not he/she continues as an employee. The single-user license is not a floating licenses or a license "by the seat". Businesses needing greater flexibility should purchase institutional subscriptions.

For machines in the subscriber's IP address range, institutional subscriptions include both unlimited access to Numerical Recipes Code (and the license for its use), and also unlimited access to Numerical Recipes Electronic, the electronic form of the Numerical Recipes book. The institutional subscription is generally the most cost-effective way to make Numerical Recipes available to work groups, companies, and universities.