21891240 has 288 divisors, whose sum is σ = 88831080. Its totient is φ = 4644864.

The previous prime is 21891227. The next prime is 21891269. The reversal of 21891240 is 4219812.

It can be written as a sum of positive squares in 4 ways, for example, as 20196036 + 1695204 = 4494^2 + 1302^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 299844 + ... + 299916.

Almost surely, 2^21891240 is an apocalyptic number.

21891240 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 21891240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (44415540).

21891240 is an abundant number, since it is smaller than the sum of its proper divisors (66939840).

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

21891240 is a wasteful number, since it uses less digits than its factorization.

21891240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 121 (or 107 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 27.

The square root of 21891240 is about 4678.8075403889. The cubic root of 21891240 is about 279.7414279562.

The spelling of 21891240 in words is "twenty-one million, eight hundred ninety-one thousand, two hundred forty".