# find the next number in the series

Myke Enriq
Ranch Hand
Posts: 115
Which one of the numbers in the series is wrong, and should be replaced?
2 - 4 - 8 - 16 - 20 - 22 - 44 - 46

Paul Clapham
Sheriff
Posts: 21416
33
20.

It should be 32.

The sequence is 2^n mod 42.

fred rosenberger
lowercase baba
Bartender
Posts: 12196
35
Paul Clapham wrote:20.

It should be 32.

The sequence is 2^n mod 42.

Then how can 46 be valid?

Paul Clapham
Sheriff
Posts: 21416
33
Umm... good question. 46 is still congruent to 256 mod 42, though.

Seetharaman Venkatasamy
Ranch Hand
Posts: 5575
past 4 hours I am thinking of this... no luck till now... let me try further ;)

Matthew Brown
Bartender
Posts: 4568
9
Change to 16 to 10. I'll leave the justification for now, but it's not a very complicated sequence.

Paul Clapham
Sheriff
Posts: 21416
33
Oh yeah, it's A099942. Pity, I was kind of attached to my "42" idea.

Seetharaman Venkatasamy
Ranch Hand
Posts: 5575
Matthew Brown wrote:Change to 16 to 10.

Hmm then I can tell the solution...
+2 next *2 => then next element is 92...