21498509 has 4 divisors (see below), whose sum is σ = 21507804. Its totient is φ = 21489216.

The previous prime is 21498461. The next prime is 21498511. The reversal of 21498509 is 90589412.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 7645225 + 13853284 = 2765^2 + 3722^2 .

It is a cyclic number.

It is not a de Polignac number, because 21498509 - 2¹² = 21494413 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21498539) 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, 1859 + ... + 6815.

It is an arithmetic number, because the mean of its divisors is an integer number (5376951).

Almost surely, 2^21498509 is an apocalyptic number.

It is an amenable number.

21498509 is a deficient number, since it is larger than the sum of its proper divisors (9295).

21498509 is an equidigital number, since it uses as much as digits as its factorization.

21498509 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9294.

The product of its (nonzero) digits is 25920, while the sum is 38.

The square root of 21498509 is about 4636.6484662955. The cubic root of 21498509 is about 278.0584603519.

The spelling of 21498509 in words is "twenty-one million, four hundred ninety-eight thousand, five hundred nine".