21644420 has 96 divisors (see below), whose sum is σ = 55910400. Its totient is φ = 6873984.

The previous prime is 21644419. The next prime is 21644423. The reversal of 21644420 is 2444612.

21644420 = 588² + 589² + ... + 644².

It is not an unprimeable number, because it can be changed into a prime (21644423) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 210089 + ... + 210191.

It is an arithmetic number, because the mean of its divisors is an integer number (582400).

Almost surely, 2^21644420 is an apocalyptic number.

21644420 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 21644420, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27955200).

21644420 is an abundant number, since it is smaller than the sum of its proper divisors (34265980).

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

21644420 is a wasteful number, since it uses less digits than its factorization.

21644420 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 217 (or 215 counting only the distinct ones).

The product of its (nonzero) digits is 1536, while the sum is 23.

The square root of 21644420 is about 4652.3563921952. The cubic root of 21644420 is about 278.6861061302.

The spelling of 21644420 in words is "twenty-one million, six hundred forty-four thousand, four hundred twenty".