21125840 has 40 divisors (see below), whose sum is σ = 49401600. Its totient is φ = 8401536.

The previous prime is 21125803. The next prime is 21125843. The reversal of 21125840 is 4852112.

It is a tau number, because it is divible by the number of its divisors (40).

It is a super-2 number, since 2×21125840² = 892602231411200, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21125843) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 15257 + ... + 16583.

It is an arithmetic number, because the mean of its divisors is an integer number (1235040).

Almost surely, 2^21125840 is an apocalyptic number.

21125840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

21125840 is the 2654-th octagonal number.

It is an amenable number.

21125840 is an abundant number, since it is smaller than the sum of its proper divisors (28275760).

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

21125840 is a wasteful number, since it uses less digits than its factorization.

21125840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1539 (or 1533 counting only the distinct ones).

The product of its (nonzero) digits is 640, while the sum is 23.

The square root of 21125840 is about 4596.2854567574. The cubic root of 21125840 is about 276.4424046755.

Adding to 21125840 its reverse (4852112), we get a palindrome (25977952).

The spelling of 21125840 in words is "twenty-one million, one hundred twenty-five thousand, eight hundred forty".