25
XXV
11001
The number 25 — factors and divisors
Deficient
25 = 5². It has 3 divisors, adding up to 31.
Its divisors, itself excluded, add up to less than the number.
Families it belongs to
Square
A number times itself — the dots lay out as a square.
Laid out as dots
It fits as 5 × 5. The more divisors, the closer to a square.
- Prime factors
- 5²
- Divisors
- 1, 5, 25
- Sum of divisors
- 31
- Sum without itself
- 6
- Coprime below it
- 20
- Digit sum
- 7
- Digital root
- 7
- Roman numeral
- XXV
- Binary
- 11001
- Octal
- 31
- Hexadecimal
- 19
- Base 36
- P
- Bits
- 5 bits
- Collatz steps
- 23 steps · peaks at 88
- Prime before
- 23
- Prime after
- 29
The grid
Ten per row, twenty rows. The filled cells are primes — you can see the multiples of 2 and 5 drop out in columns.
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Numbers either side
How to read this
- The prime factors are what the number is made of. The count and sum of divisors both follow from them.
- Add the divisors, take the number away, and you get perfect, abundant or deficient.
- The length of the binary form is the bit count. 255 taking eight digits is what a byte is.
- Collatz: halve it if even, triple it and add one if odd. The count is how many moves reach 1.
Frequently asked questions
Q. Is 25 a prime number?
No. It breaks down into 5².
Q. What are the divisors of 25?
1, 5, 25 — 3 divisors in all, adding up to 31.
Q. How is 25 written in binary?
11001, which is 5 bits. In hexadecimal it is 19.
Q. How many Collatz steps does 25 take?
It reaches 1 in 23, peaking at 88 on the way.