Insert nine dashes between the extreme digits :

= 9 __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __  2

then, pairing the consecutive digits, from left to right, add them and place them on each of the dashes.

= 9 ( 9+ 8 ) ( 8 + 7 ) ( 7 + 4 ) ( 4 + 3 ) ( 3 + 8 ) ( 8 +7 ) ( 7 + 6 ) ( 6 + 5 ) ( 5 + 2 ) 2

= 9     17       15            11         7           11          15        13          11         7       2    

= 9₁    7₁         5 ₁              1          7₁             1 ₁            5 ₁        3₁          1          7       2

= 10     8       6              1          8           2           6         4           1          7       2

= 10     8       6              1          8           2           6         4           1          7       2

Hence, your final answer is : 108618264172

You can repeat this process for any number.