21682640 has 80 divisors (see below), whose sum is σ = 59520000. Its totient is φ = 7188480.

The previous prime is 21682627. The next prime is 21682643. The reversal of 21682640 is 4628612.

It is a tau number, because it is divible by the number of its divisors (80).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21682643) 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, 16736 + ... + 17984.

It is an arithmetic number, because the mean of its divisors is an integer number (744000).

Almost surely, 2^21682640 is an apocalyptic number.

21682640 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 21682640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29760000).

21682640 is an abundant number, since it is smaller than the sum of its proper divisors (37837360).

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

21682640 is a wasteful number, since it uses less digits than its factorization.

21682640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1300 (or 1294 counting only the distinct ones).

The product of its (nonzero) digits is 4608, while the sum is 29.

The square root of 21682640 is about 4656.4621763738. The cubic root of 21682640 is about 278.8500455300.

It can be divided in two parts, 21682 and 640, that added together give a palindrome (22322).

The spelling of 21682640 in words is "twenty-one million, six hundred eighty-two thousand, six hundred forty".