21531305 has 4 divisors (see below), whose sum is σ = 25837572. Its totient is φ = 17225040.

The previous prime is 21531269. The next prime is 21531317. The reversal of 21531305 is 50313512.

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 6885376 + 14645929 = 2624^2 + 3827^2 .

It is not a de Polignac number, because 21531305 - 2⁸ = 21531049 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2153126 + ... + 2153135.

It is an arithmetic number, because the mean of its divisors is an integer number (6459393).

Almost surely, 2^21531305 is an apocalyptic number.

It is an amenable number.

21531305 is a deficient number, since it is larger than the sum of its proper divisors (4306267).

21531305 is an equidigital number, since it uses as much as digits as its factorization.

21531305 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4306266.

The product of its (nonzero) digits is 450, while the sum is 20.

The square root of 21531305 is about 4640.1837248109. The cubic root of 21531305 is about 278.1997813473.

Adding to 21531305 its reverse (50313512), we get a palindrome (71844817).

The spelling of 21531305 in words is "twenty-one million, five hundred thirty-one thousand, three hundred five".