Slot

#

is a short-hand for #1.

#n

represents the n-th argument of a pure function.

#0

represents the pure function itself.

See:

• Wikipedia - Pure function

Examples

Unused arguments are simply ignored:

>> {#1, #2, #3}&[1, 2, 3, 4, 5]
{1,2,3}

Recursive pure functions can be written using #0:

>> If(#1<=1, 1, #1 #0(#1-1))& [10]
3628800

>> # // InputForm
#1

>> #0 // InputForm
#0

>> f := # ^ 2 &
>> f(3)
9

>> #^3& /@ {1, 2, 3}
{1,8,27}

>> #1+#2&[4, 5]
9

Related terms

Function, SlotSequence