Biquadratefree
A number is said to be biquadratefree if its Prime decomposition contains no tripled factors. All Primes are thereforetrivially biquadratefree. The biquadratefree numbers are 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 17, ...(Sloane's A046100). The biquadrateful numbers (i.e., those that contain at least one biquadrate) are 16, 32, 48, 64, 80, 81, 96,... (Sloane's A046101). The number of biquadratefree numbers less than 10, 100, 1000, ... are 10, 93, 925, 9240, 92395,923939, ..., and their asymptotic density is 
, where 
is theRiemann Zeta Function.
References
Sloane, N. J. A.A046100 andA046101 in ``An On-Line Version of the Encyclopedia of Integer Sequences.''http://www.research.att.com/~njas/sequences/eisonline.html.
- Enneagonal Number
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