20639640 has 64 divisors (see below), whose sum is σ = 70767360. Its totient is φ = 4717440.

The previous prime is 20639639. The next prime is 20639669. The reversal of 20639640 is 4693602.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 20639598 and 20639607.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 11446 + ... + 13125.

It is an arithmetic number, because the mean of its divisors is an integer number (1105740).

Almost surely, 2^20639640 is an apocalyptic number.

20639640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20639640 is an abundant number, since it is smaller than the sum of its proper divisors (50127720).

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

20639640 is a wasteful number, since it uses less digits than its factorization.

20639640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24592 (or 24588 counting only the distinct ones).

The product of its (nonzero) digits is 7776, while the sum is 30.

The square root of 20639640 is about 4543.0870561767. The cubic root of 20639640 is about 274.3051991986.

The spelling of 20639640 in words is "twenty million, six hundred thirty-nine thousand, six hundred forty".