21403521 has 20 divisors (see below), whose sum is σ = 32343300. Its totient is φ = 14103936.

The previous prime is 21403483. The next prime is 21403559. The reversal of 21403521 is 12530412.

21403521 is a `hidden beast` number, since 2 + 140 + 3 + 521 = 666.

It is an interprime number because it is at equal distance from previous prime (21403483) and next prime (21403559).

It can be written as a sum of positive squares in 2 ways, for example, as 1476225 + 19927296 = 1215^2 + 4464^2 .

It is not a de Polignac number, because 21403521 - 2¹¹ = 21401473 is a prime.

It is a super-2 number, since 2×21403521² = 916221422394882, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21403494 and 21403503.

It is not an unprimeable number, because it can be changed into a prime (21403621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 5725 + ... + 8693.

It is an arithmetic number, because the mean of its divisors is an integer number (1617165).

Almost surely, 2^21403521 is an apocalyptic number.

It is an amenable number.

21403521 is a deficient number, since it is larger than the sum of its proper divisors (10939779).

21403521 is an equidigital number, since it uses as much as digits as its factorization.

21403521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3070 (or 3061 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 18.

The square root of 21403521 is about 4626.3939520970. The cubic root of 21403521 is about 277.6483355956.

Adding to 21403521 its reverse (12530412), we get a palindrome (33933933).

The spelling of 21403521 in words is "twenty-one million, four hundred three thousand, five hundred twenty-one".