21326509 has 4 divisors (see below), whose sum is σ = 21338716. Its totient is φ = 21314304.

The previous prime is 21326479. The next prime is 21326527. The reversal of 21326509 is 90562312.

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 3433609 + 17892900 = 1853^2 + 4230^2 .

It is a cyclic number.

It is not a de Polignac number, because 21326509 - 2⁵ = 21326477 is a prime.

It is a super-2 number, since 2×21326509² = 909639972254162, which contains 22 as substring.

It is a Duffinian number.

It is a plaindrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21326309) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2934 + ... + 7159.

It is an arithmetic number, because the mean of its divisors is an integer number (5334679).

Almost surely, 2^21326509 is an apocalyptic number.

It is an amenable number.

21326509 is a deficient number, since it is larger than the sum of its proper divisors (12207).

21326509 is a wasteful number, since it uses less digits than its factorization.

21326509 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12206.

The product of its (nonzero) digits is 3240, while the sum is 28.

The square root of 21326509 is about 4618.0633386735. The cubic root of 21326509 is about 277.3149332834.

The spelling of 21326509 in words is "twenty-one million, three hundred twenty-six thousand, five hundred nine".