21869509 has 4 divisors (see below), whose sum is σ = 22623660. Its totient is φ = 21115360.

The previous prime is 21869483. The next prime is 21869521. The reversal of 21869509 is 90596812.

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 13764100 + 8105409 = 3710^2 + 2847^2 .

It is a cyclic number.

It is not a de Polignac number, because 21869509 - 2⁷ = 21869381 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21869569) 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, 377032 + ... + 377089.

It is an arithmetic number, because the mean of its divisors is an integer number (5655915).

Almost surely, 2^21869509 is an apocalyptic number.

21869509 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

It is an amenable number.

21869509 is a deficient number, since it is larger than the sum of its proper divisors (754151).

21869509 is an equidigital number, since it uses as much as digits as its factorization.

21869509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 754150.

The product of its (nonzero) digits is 38880, while the sum is 40.

The square root of 21869509 is about 4676.4846840335. The cubic root of 21869509 is about 279.6488327202.

The spelling of 21869509 in words is "twenty-one million, eight hundred sixty-nine thousand, five hundred nine".