21780396 has 36 divisors (see below), whose sum is σ = 60062184. Its totient is φ = 6600000.

The previous prime is 21780377. The next prime is 21780431. The reversal of 21780396 is 69308712.

It is a tau number, because it is divible by the number of its divisors (36).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a self number, because there is not a number n which added to its sum of digits gives 21780396.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 27105 + ... + 27896.

It is an arithmetic number, because the mean of its divisors is an integer number (1668394).

Almost surely, 2^21780396 is an apocalyptic number.

It is an amenable number.

21780396 is an abundant number, since it is smaller than the sum of its proper divisors (38281788).

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

21780396 is a wasteful number, since it uses less digits than its factorization.

21780396 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 55022 (or 55017 counting only the distinct ones).

The product of its (nonzero) digits is 18144, while the sum is 36.

The square root of 21780396 is about 4666.9471820452. The cubic root of 21780396 is about 279.2684816813.

The spelling of 21780396 in words is "twenty-one million, seven hundred eighty thousand, three hundred ninety-six".