21124404 has 72 divisors (see below), whose sum is σ = 64628928. Its totient is φ = 5679360.

The previous prime is 21124391. The next prime is 21124459. The reversal of 21124404 is 40442112.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1819 + ... + 6749.

It is an arithmetic number, because the mean of its divisors is an integer number (897624).

Almost surely, 2^21124404 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21124404, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32314464).

21124404 is an abundant number, since it is smaller than the sum of its proper divisors (43504524).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21124404 is a wasteful number, since it uses less digits than its factorization.

21124404 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4965 (or 4960 counting only the distinct ones).

The product of its (nonzero) digits is 256, while the sum is 18.

The square root of 21124404 is about 4596.1292410027. The cubic root of 21124404 is about 276.4361409358.

Adding to 21124404 its reverse (40442112), we get a palindrome (61566516).

It can be divided in two parts, 21124 and 404, that added together give a triangular number (21528 = T₂₀₇).

The spelling of 21124404 in words is "twenty-one million, one hundred twenty-four thousand, four hundred four".