21047640 has 64 divisors (see below), whose sum is σ = 64627200. Its totient is φ = 5480832.

The previous prime is 21047629. The next prime is 21047647. The reversal of 21047640 is 4674012.

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 21047640.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21047647) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3121 + ... + 7199.

It is an arithmetic number, because the mean of its divisors is an integer number (1009800).

Almost surely, 2^21047640 is an apocalyptic number.

21047640 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 21047640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32313600).

21047640 is an abundant number, since it is smaller than the sum of its proper divisors (43579560).

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

21047640 is a wasteful number, since it uses less digits than its factorization.

21047640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4136 (or 4132 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 24.

The square root of 21047640 is about 4587.7707004601. The cubic root of 21047640 is about 276.1008872934.

The spelling of 21047640 in words is "twenty-one million, forty-seven thousand, six hundred forty".