129
CXXIX
10000001
The number 129 — factors and divisors
Deficient
129 = 3 × 43. It has 4 divisors, adding up to 176.
Its divisors, itself excluded, add up to less than the number.
Laid out as dots
It fits as 3 × 43. The more divisors, the closer to a square.
- Prime factors
- 3 × 43
- Divisors
- 1, 3, 43, 129
- Sum of divisors
- 176
- Sum without itself
- 47
- Coprime below it
- 84
- Digit sum
- 12
- Digital root
- 3
- Roman numeral
- CXXIX
- Binary
- 10000001
- Octal
- 201
- Hexadecimal
- 81
- Base 36
- 3L
- Bits
- 8 bits
- Collatz steps
- 121 steps · peaks at 9,232
- Prime before
- 127
- Prime after
- 131
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 129 a prime number?
No. It breaks down into 3 × 43.
Q. What are the divisors of 129?
1, 3, 43, 129 — 4 divisors in all, adding up to 176.
Q. How is 129 written in binary?
10000001, which is 8 bits. In hexadecimal it is 81.
Q. How many Collatz steps does 129 take?
It reaches 1 in 121, peaking at 9,232 on the way.