21557020 has 96 divisors (see below), whose sum is σ = 52254720. Its totient is φ = 7418880.

The previous prime is 21557017. The next prime is 21557023. The reversal of 21557020 is 2075512.

It is an interprime number because it is at equal distance from previous prime (21557017) and next prime (21557023).

It is a super-2 number, since 2×21557020² = 929410222560800, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21556982 and 21557000.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21557023) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 303585 + ... + 303655.

It is an arithmetic number, because the mean of its divisors is an integer number (544320).

Almost surely, 2^21557020 is an apocalyptic number.

21557020 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 21557020, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26127360).

21557020 is an abundant number, since it is smaller than the sum of its proper divisors (30697700).

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

21557020 is a wasteful number, since it uses less digits than its factorization.

21557020 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 163 (or 161 counting only the distinct ones).

The product of its (nonzero) digits is 700, while the sum is 22.

The square root of 21557020 is about 4642.9538011917. The cubic root of 21557020 is about 278.3104893184.

The spelling of 21557020 in words is "twenty-one million, five hundred fifty-seven thousand, twenty".