21391240 has 64 divisors (see below), whose sum is σ = 53544960. Its totient is φ = 7637760.

The previous prime is 21391213. The next prime is 21391259. The reversal of 21391240 is 4219312.

It is a plaindrome in base 16.

It is a congruent number.

It is an unprimeable number.

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, 15457 + ... + 16783.

It is an arithmetic number, because the mean of its divisors is an integer number (836640).

Almost surely, 2^21391240 is an apocalyptic number.

21391240 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 21391240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26772480).

21391240 is an abundant number, since it is smaller than the sum of its proper divisors (32153720).

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

21391240 is a wasteful number, since it uses less digits than its factorization.

21391240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1382 (or 1378 counting only the distinct ones).

The product of its (nonzero) digits is 432, while the sum is 22.

The square root of 21391240 is about 4625.0664860086. The cubic root of 21391240 is about 277.5952220357.

The spelling of 21391240 in words is "twenty-one million, three hundred ninety-one thousand, two hundred forty".