[Enigma] Number Sequence #1

in math •  7 years ago  (edited)

Hello good people,

as a math nerd I like creating number enigmas. Wanna solve some? But note that the enigmas are not copied from other sources! So some might be too easy, some might be too difficult, and some might not have a unique answer. Plz don't use any computer programs to solve it. Thx

The first post with the right answer gets my upvote (and comment). I encourage other users to upvote the corresponding solution as well. Have fun and feel free to give critique, feedback and stuff.

Greetings Schneidor


Enigma:
What is the missing number and how to compute?
[1; 3; 7; 15; 13; 9; 19; 21; *; 15]


Authors get paid when people like you upvote their post.
If you enjoyed what you read here, create your account today and start earning FREE STEEM!
Sort Order:  

Thanks for the question. Look forward to more.

!-=o0o=-!

To follow curated math content follow @math-trail.
If you wish @math-trail to follow you then read this article.

There will be. Thx

I think 25, the best equation I have so far is conditional so probably wrong but is F(n) = [F(n-1) +2^n] modulo 18 for n <4, F(n) = [F(n-1) +2^n] modulo 36 for n > 4.

First of, you are the first one who has the courage to give it a try. Nice. The solution is a single function for all n. The sequence looks like 2^n variant, but it isn't. A small hint: F(n) = ... +1.

Thanks for the tip, I've got it now- 7. You sum the digits of the previous value and then add 1.