21023664 has 40 divisors (see below), whose sum is σ = 55472640. Its totient is φ = 6858048.

The previous prime is 21023663. The next prime is 21023677. The reversal of 21023664 is 46632012.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is not an unprimeable number, because it can be changed into a prime (21023663) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2404 + ... + 6915.

It is an arithmetic number, because the mean of its divisors is an integer number (1386816).

Almost surely, 2^21023664 is an apocalyptic number.

21023664 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21023664 is an abundant number, since it is smaller than the sum of its proper divisors (34448976).

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

21023664 is a wasteful number, since it uses less digits than its factorization.

21023664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9377 (or 9371 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 24.

The square root of 21023664 is about 4585.1569220693. The cubic root of 21023664 is about 275.9960091841.

Adding to 21023664 its reverse (46632012), we get a palindrome (67655676).

The spelling of 21023664 in words is "twenty-one million, twenty-three thousand, six hundred sixty-four".