21906240 has 112 divisors (see below), whose sum is σ = 73273920. Its totient is φ = 5529600.

The previous prime is 21906233. The next prime is 21906263. The reversal of 21906240 is 4260912.

It is a hoax number, since the sum of its digits (24) coincides with the sum of the digits of its distinct prime factors.

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 21906240.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 17640 + ... + 18840.

Almost surely, 2^21906240 is an apocalyptic number.

21906240 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 21906240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36636960).

21906240 is an abundant number, since it is smaller than the sum of its proper divisors (51367680).

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

21906240 is a wasteful number, since it uses less digits than its factorization.

21906240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1240 (or 1230 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 24.

The square root of 21906240 is about 4680.4102384300. The cubic root of 21906240 is about 279.8053068317.

The spelling of 21906240 in words is "twenty-one million, nine hundred six thousand, two hundred forty".