consecutive combination of numbers from a list

any quick methods to obtain a count of complete consecutive n numbers from a array list 1:m e.g. a list 1:21 and n=3 so

it would be 1:3,4:6,7:9,10:12,13:15,16:18,19:21,2:4,5:6,...17:19,3:5,...18:20= 19 combinations.

Answer 1

[Bruno Luong]

>> (1:19)'+(0:2) % (1:m-n+1)'+(0:n-1)

ans =

     1     2     3
     2     3     4
     3     4     5
     4     5     6
     5     6     7
     6     7     8
     7     8     9
     8     9    10
     9    10    11
    10    11    12
    11    12    13
    12    13    14
    13    14    15
    14    15    16
    15    16    17
    16    17    18
    17    18    19
    18    19    20
    19    20    21