21787220 has 48 divisors (see below), whose sum is σ = 56316288. Its totient is φ = 6894720.

The previous prime is 21787219. The next prime is 21787223. The reversal of 21787220 is 2278712.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21787223) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4166 + ... + 7805.

It is an arithmetic number, because the mean of its divisors is an integer number (1173256).

Almost surely, 2^21787220 is an apocalyptic number.

21787220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21787220 is an abundant number, since it is smaller than the sum of its proper divisors (34529068).

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

21787220 is a wasteful number, since it uses less digits than its factorization.

21787220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12000 (or 11998 counting only the distinct ones).

The product of its (nonzero) digits is 3136, while the sum is 29.

The square root of 21787220 is about 4667.6782236997. The cubic root of 21787220 is about 279.2976444374.

The spelling of 21787220 in words is "twenty-one million, seven hundred eighty-seven thousand, two hundred twenty".