21720378 has 16 divisors (see below), whose sum is σ = 44177760. Its totient is φ = 7117296.

The previous prime is 21720371. The next prime is 21720389. The reversal of 21720378 is 87302712.

It is not an unprimeable number, because it can be changed into a prime (21720371) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 30325 + ... + 31032.

It is an arithmetic number, because the mean of its divisors is an integer number (2761110).

Almost surely, 2^21720378 is an apocalyptic number.

21720378 is an abundant number, since it is smaller than the sum of its proper divisors (22457382).

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

21720378 is a wasteful number, since it uses less digits than its factorization.

21720378 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 61421.

The product of its (nonzero) digits is 4704, while the sum is 30.

The square root of 21720378 is about 4660.5126327476. The cubic root of 21720378 is about 279.0117285443.

The spelling of 21720378 in words is "twenty-one million, seven hundred twenty thousand, three hundred seventy-eight".