5
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1, 15, 9, 14, 18, 20, 25, 6?

What is the next number in the sequence?

Note: This sequence is not in the OEIS

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10
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The next number is:

$a_{n+1}$ is n-th letter of $a_n$ encoded with A1Z26.

$a_1 = 1 \rightarrow$ "one" $\rightarrow$ the first letter is O $\rightarrow 15$

$a_2 = 15 \rightarrow$ "fifteen" $\rightarrow$ the second letter is I $\rightarrow 9$

$a_3 = 9 \rightarrow$ "nine" $\rightarrow$ the third letter is N $\rightarrow 14$

$a_4 = 14 \rightarrow$ "fourteen" $\rightarrow$ the fourth letter is R $\rightarrow 18$

$a_5 = 18 \rightarrow$ "eighteen" $\rightarrow$ the fifth letter is T $\rightarrow 20$

$a_6 = 20 \rightarrow$ "twenty" $\rightarrow$ the sixth letter is Y $\rightarrow 25$

$a_7 = 25 \rightarrow$ "twenty five" $\rightarrow$ the seventh letter is F $\rightarrow 6$

$a_8 = 6 \rightarrow$ "six" $\rightarrow$ the eighth letter doesn't exist - there is no next value in the sequence

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  • $\begingroup$ Wow, you seem to always answer all my number sequence questions. Good job! $\endgroup$ – UnidentifiedX Feb 26 at 10:03
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Here is my answer, along with some reasoning for it.

15-14=1 9+6=15 15-6=9 15-1=14 (15+9)-6=18 14+6=20 (20+6)-1=25 15-9=6 (6-1)=5

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  • $\begingroup$ Why would 6-1 be the next calculation in the series? Wouldn't any other calculation with some other numbers fit just as well? If your reasoning doesn't give an unique answer, you should consider it as a strong indication that your reasoning isn't the correct solution. $\endgroup$ – Bass Mar 19 at 3:07

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