21261840 has 40 divisors (see below), whose sum is σ = 65912448. Its totient is φ = 5669760.

The previous prime is 21261839. The next prime is 21261869. The reversal of 21261840 is 4816212.

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

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a self number, because there is not a number n which added to its sum of digits gives 21261840.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 44056 + ... + 44535.

Almost surely, 2^21261840 is an apocalyptic number.

21261840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21261840 is an abundant number, since it is smaller than the sum of its proper divisors (44650608).

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

21261840 is a wasteful number, since it uses less digits than its factorization.

21261840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 88607 (or 88601 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 24.

The square root of 21261840 is about 4611.0562781211. The cubic root of 21261840 is about 277.0343460737.

The spelling of 21261840 in words is "twenty-one million, two hundred sixty-one thousand, eight hundred forty".