# Questions tagged [formation-of-numbers]

For puzzles about forming numbers using other numbers and mathematical operations. Use with [mathematics]

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### Powerful number systems

Imagine I have two positive integers, $a$ and $b$. Can you find the last digit of the sum $a+b$ given only the last digits of $a$ and $b$? More generally, can you find the last $n$ digits of $a+b$ ...
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### I'm a number with a special product, so name me when you think you've got it

In the blocks that come before, their special product tells us more. To guess my scheme you'll need calculation, but only little tests of recreation. Each block contains atoms strong as Thor, ...
• 2,296
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### Even and primes puzzle?

These are secret numbers that increase regularly. What are the next two numbers? If you like numbers, it will be fun. $2^3 \times224299$ $2^2 \times 3^2 \times 19 \times 3557$ \$2 \times 5 \times ...
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### encode in encode

Today, a cryptic message was received by Area 51: Bananatexteismarvellous605185682252125223459314283216133301 2 The staff managed to figure out that some 2 digit ...
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### Do puzzles like "write 120 using four 8" have a specific name?

Here on puzzling SE there is the category "calculation puzzle", but it's very broad. I'd like to know if somebody gave a specific name for such puzzles.
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