21778720 has 48 divisors (see below), whose sum is σ = 52133760. Its totient is φ = 8596224.

The previous prime is 21778703. The next prime is 21778721. The reversal of 21778720 is 2787712.

It is not an unprimeable number, because it can be changed into a prime (21778721) 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, 11779 + ... + 13501.

It is an arithmetic number, because the mean of its divisors is an integer number (1086120).

Almost surely, 2^21778720 is an apocalyptic number.

21778720 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 21778720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26066880).

21778720 is an abundant number, since it is smaller than the sum of its proper divisors (30355040).

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

21778720 is a wasteful number, since it uses less digits than its factorization.

21778720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1817 (or 1809 counting only the distinct ones).

The product of its (nonzero) digits is 10976, while the sum is 34.

The square root of 21778720 is about 4666.7676179557. The cubic root of 21778720 is about 279.2613182673.

The spelling of 21778720 in words is "twenty-one million, seven hundred seventy-eight thousand, seven hundred twenty".