21879840 has 96 divisors (see below), whose sum is σ = 69914880. Its totient is φ = 5750784.

The previous prime is 21879827. The next prime is 21879841. The reversal of 21879840 is 4897812.

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

It is not an unprimeable number, because it can be changed into a prime (21879841) 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, 37632 + ... + 38208.

It is an arithmetic number, because the mean of its divisors is an integer number (728280).

Almost surely, 2^21879840 is an apocalyptic number.

21879840 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 21879840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34957440).

21879840 is an abundant number, since it is smaller than the sum of its proper divisors (48035040).

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

21879840 is a wasteful number, since it uses less digits than its factorization.

21879840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 674 (or 666 counting only the distinct ones).

The product of its (nonzero) digits is 32256, while the sum is 39.

The square root of 21879840 is about 4677.5891226143. The cubic root of 21879840 is about 279.6928604925.

It can be divided in two parts, 2187 and 9840, that multiplied together give a triangular number (21520080 = T₆₅₆₀).

The spelling of 21879840 in words is "twenty-one million, eight hundred seventy-nine thousand, eight hundred forty".