21812640 has 96 divisors (see below), whose sum is σ = 71124480. Its totient is φ = 5612544.

The previous prime is 21812639. The next prime is 21812641. The reversal of 21812640 is 4621812.

It is an interprime number because it is at equal distance from previous prime (21812639) and next prime (21812641).

It is a tau number, because it is divible by the number of its divisors (96).

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

It is a self number, because there is not a number n which added to its sum of digits gives 21812640.

It is not an unprimeable number, because it can be changed into a prime (21812641) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 13137 + ... + 14703.

It is an arithmetic number, because the mean of its divisors is an integer number (740880).

Almost surely, 2^21812640 is an apocalyptic number.

21812640 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 21812640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35562240).

21812640 is an abundant number, since it is smaller than the sum of its proper divisors (49311840).

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

21812640 is a wasteful number, since it uses less digits than its factorization.

21812640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1614 (or 1606 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 24.

The square root of 21812640 is about 4670.4004110997. The cubic root of 21812640 is about 279.4062247079.

The spelling of 21812640 in words is "twenty-one million, eight hundred twelve thousand, six hundred forty".