21664500 has 192 divisors, whose sum is σ = 74850048. Its totient is φ = 4800000.

The previous prime is 21664483. The next prime is 21664501. The reversal of 21664500 is 546612.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664501) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 214450 + ... + 214550.

It is an arithmetic number, because the mean of its divisors is an integer number (389844).

Almost surely, 2^21664500 is an apocalyptic number.

21664500 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 21664500, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37425024).

21664500 is an abundant number, since it is smaller than the sum of its proper divisors (53185548).

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

21664500 is a wasteful number, since it uses less digits than its factorization.

21664500 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 147 (or 135 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 24.

The square root of 21664500 is about 4654.5139381035. The cubic root of 21664500 is about 278.7722605507.

It can be divided in two parts, 2166 and 4500, that added together give a palindrome (6666).

The spelling of 21664500 in words is "twenty-one million, six hundred sixty-four thousand, five hundred".