21901644 has 96 divisors (see below), whose sum is σ = 61286400. Its totient is φ = 6739200.

The previous prime is 21901639. The next prime is 21901703. The reversal of 21901644 is 44610912.

21901644 is a `hidden beast` number, since 2 + 19 + 0 + 1 + 644 = 666.

It is a Harshad number since it is a multiple of its sum of digits (27).

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 31 ways as a sum of consecutive naturals, for example, 144969 + ... + 145119.

It is an arithmetic number, because the mean of its divisors is an integer number (638400).

Almost surely, 2^21901644 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 21901644, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30643200).

21901644 is an abundant number, since it is smaller than the sum of its proper divisors (39384756).

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

21901644 is a wasteful number, since it uses less digits than its factorization.

21901644 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 260 (or 252 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 21901644 is about 4679.9192300722. The cubic root of 21901644 is about 279.7857374436.

The spelling of 21901644 in words is "twenty-one million, nine hundred one thousand, six hundred forty-four".