Geometry and Topology of DNA,  James White

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Linking number is a link invariant (from Brian Sanderson's knot theory course)

White, James H. An introduction to the geometry and topology of DNA structure. Mathematical methods for DNA sequences, 225--253, CRC.

figures 18 - 21, Examples
 
 

DNA Sequence and Three-dimensional Structure, Wilma Olson

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DNA Computation, Leonard Adleman

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Jonoska N, Karl SA, Saito M.Three dimensional DNA structures in computing, Biosystems. 1999 Oct;52(1-3):143-53.