21645940 has 24 divisors (see below), whose sum is σ = 47849760. Its totient is φ = 8202528.

The previous prime is 21645937. The next prime is 21646003. The reversal of 21645940 is 4954612.

It is a congruent number.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 28102 + ... + 28861.

It is an arithmetic number, because the mean of its divisors is an integer number (1993740).

Almost surely, 2^21645940 is an apocalyptic number.

21645940 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21645940 is an abundant number, since it is smaller than the sum of its proper divisors (26203820).

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

21645940 is a wasteful number, since it uses less digits than its factorization.

21645940 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 56991 (or 56989 counting only the distinct ones).

The product of its (nonzero) digits is 8640, while the sum is 31.

The square root of 21645940 is about 4652.5197474057. The cubic root of 21645940 is about 278.6926296432.

The spelling of 21645940 in words is "twenty-one million, six hundred forty-five thousand, nine hundred forty".