What is the rule for this sequence

There was no answer in the book for this but I want to know of I am right.......



4,9,19,39,79


And

100,99,97,94,90

Thank you :)

1) n(i) = [n(i-1)x2]+1

2) n(i) = [n(i-1)-i]

The first sequence doubles the number and then adds 1.
4x2=8+1=9; 9x2=18+1=19; 19x2=39+1=39; 39x2=78+1=79

The second sequence subtracts the next highest integer from the number before it.
100-1=99; 99-2=97, 97-3=94, 94-4=90