Kaprekar Number
Consider an 
-digit number 
. Square it and add the right digits to the left or 
digits. If theresultant sum is , then is called a Kaprekar number. The first few are 1, 9, 45, 55, 99, 297, 703, ... (Sloane's A006886).
See also Digital Root, Digitaddition, Happy Number, Kaprekar Routine, Narcissistic Number,Recurring Digital Invariant
References
Sloane, N. J. A. SequenceA006886/M4625in ``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.
- Cylindrical Segment
- Cylindrical Wedge
- Cylindroid
- Daisy
- d'Alembertian Operator
- d'Alembert Ratio Test
- d'Alembert's Equation
- d'Alembert's Solution
- d'Alembert's Theorem
- Damped Exponential Cosine Integral
- d-Analog
- Dandelin Spheres
- Danielson-Lanczos Lemma
- Darboux Integral
- Darboux-Stieltjes Integral
- Darboux Vector
- Darling's Products
- Dart
- Darwin-de Sitter Spheroid
- Darwin's Expansions
- Database
- Data Structure
- Daubechies Wavelet Filter
- Davenport-Schinzel Sequence
- Dawson's Integral