21125664 has 144 divisors (see below), whose sum is σ = 71820000. Its totient is φ = 6023808.

The previous prime is 21125651. The next prime is 21125669. The reversal of 21125664 is 46652112.

It is a tau number, because it is divible by the number of its divisors (144).

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

It is not an unprimeable number, because it can be changed into a prime (21125669) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 42087 + ... + 42585.

It is an arithmetic number, because the mean of its divisors is an integer number (498750).

Almost surely, 2^21125664 is an apocalyptic number.

21125664 is a gapful number since it is divisible by the number (24) 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 21125664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35910000).

21125664 is an abundant number, since it is smaller than the sum of its proper divisors (50694336).

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

21125664 is a wasteful number, since it uses less digits than its factorization.

21125664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 532 (or 511 counting only the distinct ones).

The product of its digits is 2880, while the sum is 27.

The square root of 21125664 is about 4596.2663108223. The cubic root of 21125664 is about 276.4416369901.

Adding to 21125664 its reverse (46652112), we get a palindrome (67777776).

It can be divided in two parts, 2112 and 5664, that added together give a 5-th power (7776 = 6⁵).

The spelling of 21125664 in words is "twenty-one million, one hundred twenty-five thousand, six hundred sixty-four".