21523968 has 120 divisors (see below), whose sum is σ = 64792728. Its totient is φ = 7133184.

The previous prime is 21523961. The next prime is 21523969. The reversal of 21523968 is 86932512.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21523961) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 124330 + ... + 124502.

Almost surely, 2^21523968 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 21523968, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32396364).

21523968 is an abundant number, since it is smaller than the sum of its proper divisors (43268760).

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

21523968 is an frugal number, since it uses more digits than its factorization.

21523968 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 206 (or 178 counting only the distinct ones).

The product of its digits is 25920, while the sum is 36.

The square root of 21523968 is about 4639.3930637531. The cubic root of 21523968 is about 278.1681780037.

The spelling of 21523968 in words is "twenty-one million, five hundred twenty-three thousand, nine hundred sixty-eight".