a frequent number thrown out there is how many neurons and how many connections does a human brain have. citing this old source [1] and assuming a fully connected brain (an impossible hypothesis due to natural synapse pruning in brains)

a) total neurons
N = 1010

b) total synapses (links)
S = 1015

c) total combinations with no pruning (i.e., everything connected to everything), considering neurons nodes and synapses paths (graph theory).
C = (N*S-1)! = (1010 * 1015 - 1)! = 101028.42432135416435

where ! is the factorial operator

it's a fucking huge number! just so you get how big it is, there are an estimated 1060 to 1080 atoms in the universe[2], so effectively, what is commonly thrown around is true: there are more possible combinations of brain sequences than there are atoms in the universe. in fact, something like 101028.42432135416435 times more!

note that this is grossly overestimated as
1) some brain structures loop, leading to more combinations than what this predicts
2) not sure if the graph assumption is accurate as a mathematical model
3) no pruning included, meaning connectivity is assumed to be the maximum possible

the next time someone tells you "the brain isn't everything", tell them that the brain can represent a gajillion more "everythings" than the whole number of atoms in the universe. this is my naive take, as [1] has it covered with real science.

math results by wolfram alpha

godspeed starstuff ☆★☆☆★★★☆☆☆☆☆

[1] http://www.springerlink.com/content/k24887l86u411w02/
[2] http://en.wikipedia.org/wiki/Observable_universe and STFG