An Easy Sequence?


Can you name the number that would complete this peculiar eight-term sequence?

19, 5, 17, 21, 5, 14, 3, ?


This is supposed to be an easy sequence but you won’t be able to solve it if you only try to find some sort of mathematical patterns, which is a common mistake made by many who tried to solve this type of puzzle. The problem actually hints about the solution. It’s an eight-term sequence and SEQUENCE has eight letters. So, the eight numbers in the sequence correspond to the positions of the letters in the word SEQUENCE in the English alphabet.

Thus, the first term of the sequence, 19, represents the position of the letter “S”, which is the nineteenth letter. E is the fifth letter, Q is the seventeenth letter, and so on.

So, the missing number is 5.



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My name Edmark M. Law. I work as a freelance writer, mainly writing about science and mathematics. I am an ardent hobbyist. I like to read, solve puzzles, play chess, make origami and play basketball. In addition, I dabble in magic, particularly card magic and other sleight-of-hand type magic. I live in Hong Kong. You can find me on Twitter` and Facebook. My email is

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