21605620 has 12 divisors (see below), whose sum is σ = 45371844. Its totient is φ = 8642240.

The previous prime is 21605611. The next prime is 21605627. The reversal of 21605620 is 2650612.

It can be written as a sum of positive squares in 2 ways, for example, as 2630884 + 18974736 = 1622^2 + 4356^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21605591 and 21605600.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21605627) 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 3 ways as a sum of consecutive naturals, for example, 540121 + ... + 540160.

It is an arithmetic number, because the mean of its divisors is an integer number (3780987).

Almost surely, 2^21605620 is an apocalyptic number.

21605620 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21605620 is an abundant number, since it is smaller than the sum of its proper divisors (23766224).

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

21605620 is a wasteful number, since it uses less digits than its factorization.

21605620 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1080290 (or 1080288 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 22.

The square root of 21605620 is about 4648.1845918595. The cubic root of 21605620 is about 278.5194813753.

The spelling of 21605620 in words is "twenty-one million, six hundred five thousand, six hundred twenty".