21775129 has 4 divisors (see below), whose sum is σ = 22363684. Its totient is φ = 21186576.

The previous prime is 21775123. The next prime is 21775139. The reversal of 21775129 is 92157712.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 12411529 + 9363600 = 3523^2 + 3060^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21775129 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21775094 and 21775103.

It is not an unprimeable number, because it can be changed into a prime (21775123) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 294222 + ... + 294295.

It is an arithmetic number, because the mean of its divisors is an integer number (5590921).

Almost surely, 2^21775129 is an apocalyptic number.

It is an amenable number.

21775129 is a deficient number, since it is larger than the sum of its proper divisors (588555).

21775129 is an equidigital number, since it uses as much as digits as its factorization.

21775129 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 588554.

The product of its digits is 8820, while the sum is 34.

The square root of 21775129 is about 4666.3828604177. The cubic root of 21775129 is about 279.2459686888.

It can be divided in two parts, 21775 and 129, that added together give a square (21904 = 148²).

The spelling of 21775129 in words is "twenty-one million, seven hundred seventy-five thousand, one hundred twenty-nine".