21256440 has 64 divisors (see below), whose sum is σ = 67132800. Its totient is φ = 5369472.

The previous prime is 21256399. The next prime is 21256447. The reversal of 21256440 is 4465212.

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 21256440.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21256447) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2382 + ... + 6941.

It is an arithmetic number, because the mean of its divisors is an integer number (1048950).

Almost surely, 2^21256440 is an apocalyptic number.

21256440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21256440 is an abundant number, since it is smaller than the sum of its proper divisors (45876360).

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

21256440 is a wasteful number, since it uses less digits than its factorization.

21256440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9356 (or 9352 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 24.

The square root of 21256440 is about 4610.4706918058. The cubic root of 21256440 is about 277.0108907168.

The spelling of 21256440 in words is "twenty-one million, two hundred fifty-six thousand, four hundred forty".