21023640 has 96 divisors (see below), whose sum is σ = 74552400. Its totient is φ = 5095680.

The previous prime is 21023623. The next prime is 21023641. The reversal of 21023640 is 4632012.

It is a happy number.

21023640 is a `hidden beast` number, since 2 + 1 + 0 + 23 + 640 = 666.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21023641) 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, 1306 + ... + 6614.

Almost surely, 2^21023640 is an apocalyptic number.

21023640 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 21023640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37276200).

21023640 is an abundant number, since it is smaller than the sum of its proper divisors (53528760).

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

21023640 is a wasteful number, since it uses less digits than its factorization.

21023640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5337 (or 5330 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 18.

The square root of 21023640 is about 4585.1543049280. The cubic root of 21023640 is about 275.9959041610.

Adding to 21023640 its reverse (4632012), we get a palindrome (25655652).

It can be divided in two parts, 210236 and 40, that added together give a triangular number (210276 = T₆₄₈).

The spelling of 21023640 in words is "twenty-one million, twenty-three thousand, six hundred forty".