20664864 has 108 divisors (see below), whose sum is σ = 64702638. Its totient is φ = 6251520.

The previous prime is 20664851. The next prime is 20664869. The reversal of 20664864 is 46846602.

It is a happy number.

20664864 is a `hidden beast` number, since 2 + 0 + 6 + 648 + 6 + 4 = 666.

It can be written as a sum of positive squares in only one way, i.e., 16744464 + 3920400 = 4092^2 + 1980^2 .

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20664869) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 34552 + ... + 35144.

Almost surely, 2^20664864 is an apocalyptic number.

20664864 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 20664864, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32351319).

20664864 is an abundant number, since it is smaller than the sum of its proper divisors (44037774).

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

20664864 is a wasteful number, since it uses less digits than its factorization.

20664864 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 631 (or 609 counting only the distinct ones).

The product of its (nonzero) digits is 55296, while the sum is 36.

The square root of 20664864 is about 4545.8622944388. The cubic root of 20664864 is about 274.4168978139.

It can be divided in two parts, 20664 and 864, that added together give a triangular number (21528 = T₂₀₇).

The spelling of 20664864 in words is "twenty million, six hundred sixty-four thousand, eight hundred sixty-four".