Hofstadter G-Sequence
The sequence defined by 
and
The first few terms are 1, 1, 2, 3, 3, 4, 4, 5, 6, 6, 7, 8, 8, 9, 9, ... (Sloane's A005206).
References
Hofstadter, D. R. Gödel, Escher, Bach: An Eternal Golden Braid. New York: Vintage Books, p. 137, 1989. Sloane, N. J. A. SequenceA005206/M0436in ``An On-Line Version of the Encyclopedia of Integer Sequences.''http://www.research.att.com/~njas/sequences/eisonline.html and Sloane, N. J. A. and Plouffe, S.The Encyclopedia of Integer Sequences. San Diego: Academic Press, 1995.
- Extremum
- Extremum Test
- Extrinsic Curvature
- Fabry Imbedding
- Face
- Facet
- Faceting
- Factor
- Factor Base
- Factor (Graph)
- Factor Group
- Factorial
- Factorial Moment
- Factorial Number
- Factorial Prime
- Factorial Sum
- Factoring
- Factorion
- Factorization
- Factor Level
- Factor Ring
- Factor Space
- Fagnano's Point
- Fagnano's Problem
- Fagnano's Theorem