Finally decided to post my comment as a solution.
Please note first, I'm not familar with Java, so take care with my comment/syntax.
a.) I'm missing the sum you like to calculate/return
b.) Your for Loop seems to miss the first element.
Think about somthing like this:
var sum= 0;
for (var i= 0; i< array.length;i++)
sum= sum + (i+1) * Array[i];
// At this point, sum should have the value you excpect.
Do you see the differences?