21786240 has 128 divisors (see below), whose sum is σ = 79413120. Its totient is φ = 4976640.

The previous prime is 21786223. The next prime is 21786241. The reversal of 21786240 is 4268712.

It is a tau number, because it is divible by the number of its divisors (128).

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 21786198 and 21786207.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21786241) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 12630 + ... + 14250.

It is an arithmetic number, because the mean of its divisors is an integer number (620415).

Almost surely, 2^21786240 is an apocalyptic number.

21786240 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 21786240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39706560).

21786240 is an abundant number, since it is smaller than the sum of its proper divisors (57626880).

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

21786240 is a wasteful number, since it uses less digits than its factorization.

21786240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1650 (or 1638 counting only the distinct ones).

The product of its (nonzero) digits is 5376, while the sum is 30.

The square root of 21786240 is about 4667.5732452743. The cubic root of 21786240 is about 279.2934567256.

The spelling of 21786240 in words is "twenty-one million, seven hundred eighty-six thousand, two hundred forty".