The Association of Digital Forensics, Security and Law (ADFSL)
Although one is unlikely to ever want to brute-force an Android lock pattern, many do wonder about the relative strength of the lock pattern versus a multidigit personal identification number (PIN). It becomes obvious pretty quickly that there are many more lock patterns than the 10,000 possible four-digit PINs.
Ponstein, J. (1966, May). Self-avoiding paths and the adjacency matrix of a graph. SIAM Journal on Applied Mathematics, 14(3), 600-609.
Kessler, Gary C.
"Technology Corner: Calculating the Number of Android Lock Patterns: An Unfinished Study in Number Theory,"
Journal of Digital Forensics, Security and Law: Vol. 8
, Article 4.
Available at: http://commons.erau.edu/jdfsl/vol8/iss4/4