21782640 has 160 divisors (see below), whose sum is σ = 75995136. Its totient is φ = 5114880.

The previous prime is 21782503. The next prime is 21782647. The reversal of 21782640 is 4628712.

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 = 21782598 and 21782607.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21782647) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 97569 + ... + 97791.

Almost surely, 2^21782640 is an apocalyptic number.

21782640 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 21782640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37997568).

21782640 is an abundant number, since it is smaller than the sum of its proper divisors (54212496).

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

21782640 is a wasteful number, since it uses less digits than its factorization.

21782640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 287 (or 281 counting only the distinct ones).

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

The square root of 21782640 is about 4667.1875899732. The cubic root of 21782640 is about 279.2780722163.

It can be divided in two parts, 21782 and 640, that added together give a palindrome (22422).

The spelling of 21782640 in words is "twenty-one million, seven hundred eighty-two thousand, six hundred forty".