21780799 has 4 divisors (see below), whose sum is σ = 22312080. Its totient is φ = 21249520.

The previous prime is 21780779. The next prime is 21780809. The reversal of 21780799 is 99708712.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21780799 - 2¹³ = 21772607 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21780709) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 265579 + ... + 265660.

It is an arithmetic number, because the mean of its divisors is an integer number (5578020).

Almost surely, 2^21780799 is an apocalyptic number.

21780799 is a deficient number, since it is larger than the sum of its proper divisors (531281).

21780799 is an equidigital number, since it uses as much as digits as its factorization.

21780799 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 531280.

The product of its (nonzero) digits is 63504, while the sum is 43.

The square root of 21780799 is about 4666.9903578216. The cubic root of 21780799 is about 279.2702040942.

The spelling of 21780799 in words is "twenty-one million, seven hundred eighty thousand, seven hundred ninety-nine".