20809836 has 72 divisors (see below), whose sum is σ = 57264480. Its totient is φ = 6345216.

The previous prime is 20809813. The next prime is 20809847. The reversal of 20809836 is 63890802.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a self number, because there is not a number n which added to its sum of digits gives 20809836.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 22185 + ... + 23103.

It is an arithmetic number, because the mean of its divisors is an integer number (795340).

Almost surely, 2^20809836 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20809836, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28632240).

20809836 is an abundant number, since it is smaller than the sum of its proper divisors (36454644).

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

20809836 is a wasteful number, since it uses less digits than its factorization.

20809836 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 983 (or 978 counting only the distinct ones).

The product of its (nonzero) digits is 20736, while the sum is 36.

The square root of 20809836 is about 4561.7799157785. The cubic root of 20809836 is about 275.0571165109.

The spelling of 20809836 in words is "twenty million, eight hundred nine thousand, eight hundred thirty-six".