Compute the Adler-32 checksum
Mathematica, 46 bytes

{1,4^8}.Fold[##+{0,#&amp;@@#}&amp;,{1,0},#]~Mod~65521&amp;


An anonymous function that takes an integer array and returns the Adler-32, with some improvements from miles and Martin (see comments).

miles' is also 46 bytes, but faster:

{1,4^8}.{Tr@#+1,Tr[Accumulate@#+1]}~Mod~65521&amp;