21457644 has 48 divisors (see below), whose sum is σ = 54227712. Its totient is φ = 6564672.

The previous prime is 21457627. The next prime is 21457649. The reversal of 21457644 is 44675412.

It is not an unprimeable number, because it can be changed into a prime (21457649) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 40767 + ... + 41289.

It is an arithmetic number, because the mean of its divisors is an integer number (1129744).

Almost surely, 2^21457644 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21457644, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27113856).

21457644 is an abundant number, since it is smaller than the sum of its proper divisors (32770068).

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

21457644 is a wasteful number, since it uses less digits than its factorization.

21457644 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 806 (or 804 counting only the distinct ones).

The product of its digits is 26880, while the sum is 33.

The square root of 21457644 is about 4632.2396311072. The cubic root of 21457644 is about 277.8821680299.

The spelling of 21457644 in words is "twenty-one million, four hundred fifty-seven thousand, six hundred forty-four".