How do you calculate the number of all possible structural isomers for alkanes?

Yes we can find all possible structural isomers Of a given hydrocarbon.

Number of total structural isomers = 2^(N-4)+1

Where N is number of carbons in hydrocarbon

Example: (1)
Number of structural somers of butane (C4H10) is 

SOLUTION:

Where , n=4
=2^(4-4)+1
=2^(0)+1
=1+1
=2

Example: (2)
Number of structural somers of butane (C5H12) is.

SOLUTION:

Where , n=5
=2^(5-4)+1
=2^(1)+1
=2+1
=3

Example: (3)
Number of structural somers of butane (C6H14) is.

SOLUTION:

Where , n=6
=2^(6-4)+1
=2^(2)+1
=4+1
=5

Example: (4)
Number of structural somers of butane (C7H16) is.

SOLUTION:

Where , n=7
=2^(7-4)+1
=2^(3)+1
=8+1
=9

Example: (5)
Number of structural somers of butane (C8H18) is.

SOLUTION:

Where , n=8
=2^(8-4)+1
=2^(4)+1
=16+1
=17

Example: (5)
Number of structural somers of butane (C8H18) is.

SOLUTION:

Where , n=9
=2^(9-4)+1
=2^(5)+1
=32+1
=33