What is the First Number of the Sequence?

If a number in a numeric sequence is 17 and the second number is 3, what is the first number?

I hesitated to add this because it’s poorly worded, ambiguous and the answer could be almost anything. I prefer teasers with a single answer, but there you go.

If you came up with a different answer and can explain how you did it, don’t think you’re wrong. It’s probably just as valid. Feel free to share yours in the comments.

My answer for the first number is 2.

Here’s how I got it.

The generic rule for a number in the sequence is: 2^(n – 1) + 1, where n is the position in the sequence.

Note: The teaser doesn’t specify the position of 17. In this case, it’s fifth.

Position 1: (so n = 1) is 2^(1 – 1) + 1 = 2

Position 2: 2^(2 – 1) + 1 = 3

Position 3: 2^(3 – 1) + 1 = 5

Position 4: 2^(4 – 1) + 1 = 9

Position 5: 2^(5 – 1) + 1 = 17

For the curious, the next 5 numbers of the sequence would be:

Position 6: 2^(6 – 1) + 1 = 33

Position 7: 2^(7 – 1) + 1 = 65

Position 8: 2^(8 – 1) + 1 = 129

Position 9: 2^(9 – 1) + 1 = 257

Position 10: 2^(10 – 1) + 1 = 513

Posted in Brain Teasers

Tree That’s Difficult To Get Along With

Which tree is the most difficult to get along with?

A crab tree.

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I Change Stature As I Age

I change stature as I age, but my importance does not differ by age. My importance is manifested mostly when with my boss. When we part, I am of no importance.

What am I?

A pencil. It gets shorter with use, but is no less important. Its impact is from the person using the pencil to write or draw. Without them, the pencil is just an idle tool.

Thanks Keller!

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Singular When Adding an S

There are many English words that you can add an “s” to make it plural. But far fewer words become singular when you add an “s”. What are two examples of these much rarer words?

Cares -> Caress
Princes -> Princess

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Apples for Leather

Apples for leather,
leather for silk,
silk for tobacco,
all to get milk.

Bartering.

By Sef Daystrom

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Two More Seconds

Ida puts her coffee into the microwave, as she does every morning, for exactly two minutes. When the microwave goes off, she opens the door, but then closes the door again and sets the microwave for two more seconds. What good would two more seconds be?

To rotate the handle on the mug so she can comfortably remove it.

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I am a ship that can be made to ride the greatest waves. I am not built by objects, but built by minds. What am I?

Friendship.

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I wave my hands at you,
But I never say goodbye.

You’re always cool with me,
Even cooler when I’m high.

What am I?

An electric fan

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Odd Start, Even Finish

What three letter English word has an odd start, an even finish and an infinitely long middle?

The word vex. “v” is Roman numeral 5, which is odd. “x” is Roman numeral 10, which is even. “e” is the base of the natural logarithm and is irrational (e = 2.718281828…). Its mantissa (the part to the right of the decimal point) is infinitely long.

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I Live Above A Star

I live above a star but never burn. I have 11 neighbors but they never turn. My initials are p, q, r and sometimes s.

What am I?

Number 7 on a phone keypad.

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