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find the next number in the sequence 10,9,90,91,7000

how did we get to 7000 in the sequence above and what is the next number?
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2 Answers

I dunno, Andre.  Here's an answer equally confusing:
   (10 + 9 + 90 + 91)*35 = 7000
Then of course keep it up (minus 1, multiply, add 1, etc.):
   7000 - 1 = 6999 * 7000 = 48,993,000 + 1 = 48,993,001
so: (7000 + 6999 + 48,993,000 + 48,993,001) * 35 = 3,430,000,000
Whaddya think?
There are infinitely many answers, of course, but here is one that makes sense:
 
Write out the numbers:
 
ten
nine
ninety
ninety one
seven thousand
 
If you count the number of letters you find the sequence
3, 4, 6, 9, 13
Their difference increases by 1 every time, so the next number should have 18 letters. Except for the first, the number of syllables increases by 1 every time:
1, 1, 2, 3, 4,
so the next number could have 5 syllables.
If we just use the digits 0 and 9, the next number could be
 
99000 = ninety nine thousand