Euler Pseudoprime

An Euler pseudoprime is a composite number $n$ which satisfies

$$2^{(n-1)/2}\equiv \pm 1\ \left({{\rm mod\ } {n}}\right).$$

The first few base-2 Euler pseudoprimes are 341, 561, 1105, 1729, 1905, 2047, ... (Sloane's A006970).

See also Euler-Jacobi Pseudoprime, Pseudoprime, Strong Pseudoprime

References

Sloane, N. J. A. Sequence A006970/M5442 in ``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.