20640864 has 48 divisors (see below), whose sum is σ = 54492480. Its totient is φ = 6840960.

The previous prime is 20640847. The next prime is 20640869. The reversal of 20640864 is 46804602.

It is a tau number, because it is divible by the number of its divisors (48).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20640869) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 19747 + ... + 20765.

It is an arithmetic number, because the mean of its divisors is an integer number (1135260).

Almost surely, 2^20640864 is an apocalyptic number.

20640864 is a gapful number since it is divisible by the number (24) 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 20640864, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27246240).

20640864 is an abundant number, since it is smaller than the sum of its proper divisors (33851616).

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

20640864 is a wasteful number, since it uses less digits than its factorization.

20640864 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1243 (or 1235 counting only the distinct ones).

The product of its (nonzero) digits is 9216, while the sum is 30.

The square root of 20640864 is about 4543.2217643430. The cubic root of 20640864 is about 274.3106214981.

The spelling of 20640864 in words is "twenty million, six hundred forty thousand, eight hundred sixty-four".