Question

what is the rule for 1,3,-1,-3,-7,-21,-25

Answer 1

2 rules are following!!

first for 1, 3 is 1 * 3 = 3

second for 3, -1 is 3 - 4 = -1

then again -1 * 3 = -3 and so on..

first * +3 and second step -4

I hope you understand!! :)