21601820 has 12 divisors (see below), whose sum is σ = 45363864. Its totient is φ = 8640720.

The previous prime is 21601819. The next prime is 21601831. The reversal of 21601820 is 2810612.

It is a Harshad number since it is a multiple of its sum of digits (20), and also a Moran number because the ratio is a prime number: 1080091 = 21601820 / (2 + 1 + 6 + 0 + 1 + 8 + 2 + 0).

It is a junction number, because it is equal to n+sod(n) for n = 21601792 and 21601801.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 540026 + ... + 540065.

It is an arithmetic number, because the mean of its divisors is an integer number (3780322).

Almost surely, 2^21601820 is an apocalyptic number.

21601820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21601820 is an abundant number, since it is smaller than the sum of its proper divisors (23762044).

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

21601820 is a wasteful number, since it uses less digits than its factorization.

21601820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1080100 (or 1080098 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 20.

The square root of 21601820 is about 4647.7758121493. The cubic root of 21601820 is about 278.5031517338.

The spelling of 21601820 in words is "twenty-one million, six hundred one thousand, eight hundred twenty".