21805836 has 48 divisors (see below), whose sum is σ = 55323744. Its totient is φ = 6644736.

The previous prime is 21805831. The next prime is 21805837. The reversal of 21805836 is 63850812.

It is a happy number.

It is a junction number, because it is equal to n+sod(n) for n = 21805797 and 21805806.

It is not an unprimeable number, because it can be changed into a prime (21805831) 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, 17010 + ... + 18246.

It is an arithmetic number, because the mean of its divisors is an integer number (1152578).

Almost surely, 2^21805836 is an apocalyptic number.

21805836 is a gapful number since it is divisible by the number (26) 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 21805836, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27661872).

21805836 is an abundant number, since it is smaller than the sum of its proper divisors (33517908).

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

21805836 is a wasteful number, since it uses less digits than its factorization.

21805836 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1370 (or 1368 counting only the distinct ones).

The product of its (nonzero) digits is 11520, while the sum is 33.

The square root of 21805836 is about 4669.6719370851. The cubic root of 21805836 is about 279.3771700305.

The spelling of 21805836 in words is "twenty-one million, eight hundred five thousand, eight hundred thirty-six".