21404 has 6 divisors (see below), whose sum is σ = 37464. Its totient is φ = 10700.

The previous prime is 21401. The next prime is 21407. The reversal of 21404 is 40412.

It is an interprime number because it is at equal distance from previous prime (21401) and next prime (21407).

It is a nialpdrome in base 13.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 21404.

It is not an unprimeable number, because it can be changed into a prime (21401) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2672 + ... + 2679.

It is an arithmetic number, because the mean of its divisors is an integer number (6244).

2²¹⁴⁰⁴ is an apocalyptic number.

It is an amenable number.

21404 is a deficient number, since it is larger than the sum of its proper divisors (16060).

21404 is a wasteful number, since it uses less digits than its factorization.

21404 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5355 (or 5353 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 11.

The square root of 21404 is about 146.3010594630. The cubic root of 21404 is about 27.7650406790.

Adding to 21404 its reverse (40412), we get a palindrome (61816).

The spelling of 21404 in words is "twenty-one thousand, four hundred four", and thus it is an iban number.