20640820 has 24 divisors (see below), whose sum is σ = 44518824. Its totient is φ = 8032896.

The previous prime is 20640793. The next prime is 20640827. The reversal of 20640820 is 2804602.

It can be written as a sum of positive squares in 4 ways, for example, as 13264164 + 7376656 = 3642^2 + 2716^2 .

It is a junction number, because it is equal to n+sod(n) for n = 20640791 and 20640800.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20640827) 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 7 ways as a sum of consecutive naturals, for example, 13207 + ... + 14686.

It is an arithmetic number, because the mean of its divisors is an integer number (1854951).

Almost surely, 2^20640820 is an apocalyptic number.

20640820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20640820 is an abundant number, since it is smaller than the sum of its proper divisors (23878004).

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

20640820 is a wasteful number, since it uses less digits than its factorization.

20640820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27939 (or 27937 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 22.

The square root of 20640820 is about 4543.2169219618. The cubic root of 20640820 is about 274.3104265825.

It can be divided in two parts, 20 and 640820, that multiplied together give a square (12816400 = 3580²).

The spelling of 20640820 in words is "twenty million, six hundred forty thousand, eight hundred twenty".