21851685220 has 48 divisors (see below), whose sum is σ = 46208086848. Its totient is φ = 8679977600.

The previous prime is 21851685211. The next prime is 21851685227. The reversal of 21851685220 is 2258615812.

It is a super-2 number, since 2×21851685220² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21851685227) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2213295 + ... + 2223145.

It is an arithmetic number, because the mean of its divisors is an integer number (962668476).

Almost surely, 2^21851685220 is an apocalyptic number.

21851685220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21851685220 is an abundant number, since it is smaller than the sum of its proper divisors (24356401628).

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

21851685220 is a wasteful number, since it uses less digits than its factorization.

21851685220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10620 (or 10618 counting only the distinct ones).

The product of its (nonzero) digits is 76800, while the sum is 40.

The spelling of 21851685220 in words is "twenty-one billion, eight hundred fifty-one million, six hundred eighty-five thousand, two hundred twenty".