21139720 has 64 divisors (see below), whose sum is σ = 54961920. Its totient is φ = 7167744.

The previous prime is 21139717. The next prime is 21139747. The reversal of 21139720 is 2793112.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 28474 + ... + 29206.

It is an arithmetic number, because the mean of its divisors is an integer number (858780).

Almost surely, 2^21139720 is an apocalyptic number.

21139720 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 21139720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27480960).

21139720 is an abundant number, since it is smaller than the sum of its proper divisors (33822200).

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

21139720 is a wasteful number, since it uses less digits than its factorization.

21139720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 854 (or 850 counting only the distinct ones).

The product of its (nonzero) digits is 756, while the sum is 25.

The square root of 21139720 is about 4597.7951237523. The cubic root of 21139720 is about 276.5029337173.

The spelling of 21139720 in words is "twenty-one million, one hundred thirty-nine thousand, seven hundred twenty".