21904540 has 48 divisors (see below), whose sum is σ = 53145792. Its totient is φ = 7428096.

The previous prime is 21904523. The next prime is 21904559. The reversal of 21904540 is 4540912.

It is a super-2 number, since 2×21904540² = 959617745223200, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 12774 + ... + 14386.

It is an arithmetic number, because the mean of its divisors is an integer number (1107204).

Almost surely, 2^21904540 is an apocalyptic number.

21904540 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21904540, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26572896).

21904540 is an abundant number, since it is smaller than the sum of its proper divisors (31241252).

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

21904540 is a wasteful number, since it uses less digits than its factorization.

21904540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1726 (or 1724 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 25.

The square root of 21904540 is about 4680.2286268942. The cubic root of 21904540 is about 279.7980686912.

The spelling of 21904540 in words is "twenty-one million, nine hundred four thousand, five hundred forty".