21403553 has 4 divisors (see below), whose sum is σ = 21424788. Its totient is φ = 21382320.

The previous prime is 21403483. The next prime is 21403559. The reversal of 21403553 is 35530412.

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 19114384 + 2289169 = 4372^2 + 1513^2 .

It is a cyclic number.

It is not a de Polignac number, because 21403553 - 2¹² = 21399457 is a prime.

It is a super-2 number, since 2×21403553² = 916224162047618, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21403559) 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, 9026 + ... + 11147.

It is an arithmetic number, because the mean of its divisors is an integer number (5356197).

Almost surely, 2^21403553 is an apocalyptic number.

It is an amenable number.

21403553 is a deficient number, since it is larger than the sum of its proper divisors (21235).

21403553 is a wasteful number, since it uses less digits than its factorization.

21403553 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21234.

The product of its (nonzero) digits is 1800, while the sum is 23.

The square root of 21403553 is about 4626.3974105128. The cubic root of 21403553 is about 277.6484739644.

Adding to 21403553 its reverse (35530412), we get a palindrome (56933965).

The spelling of 21403553 in words is "twenty-one million, four hundred three thousand, five hundred fifty-three".