Find the rules and fill in the numbers 10,11,21,32,53, ()

Find the rules and fill in the numbers 10,11,21,32,53, ()


The answer is 85
The first two numbers add up to the third,
For example: 10 + 11 = 22
11+21=32
21+32=53
32+53=85



The answer is 21. Why


The first number multiplied by 2, plus the last number, equals the third number
1*2+1=3
1*2+3=5
3*2+5=11
5*2+11=21~



Find the rule 3 5 11 21 43
Let's use n!


n3=2*n1+n2
n4=2*n2+n3
Nx=2*N(x-2)+N(x-1)