21544640 has 56 divisors (see below), whose sum is σ = 55260240. Its totient is φ = 7953408.

The previous prime is 21544631. The next prime is 21544669. The reversal of 21544640 is 4644512.

It is a Harshad number since it is a multiple of its sum of digits (26).

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, 1571 + ... + 6749.

It is an arithmetic number, because the mean of its divisors is an integer number (986790).

Almost surely, 2^21544640 is an apocalyptic number.

21544640 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 21544640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27630120).

21544640 is an abundant number, since it is smaller than the sum of its proper divisors (33715600).

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

21544640 is a wasteful number, since it uses less digits than its factorization.

21544640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5209 (or 5199 counting only the distinct ones).

The product of its (nonzero) digits is 3840, while the sum is 26.

The square root of 21544640 is about 4641.6204067114. The cubic root of 21544640 is about 278.2572020576.

The spelling of 21544640 in words is "twenty-one million, five hundred forty-four thousand, six hundred forty".