20999640 has 64 divisors (see below), whose sum is σ = 63648000. Its totient is φ = 5542272.

The previous prime is 20999623. The next prime is 20999651. The reversal of 20999640 is 4699902.

It is a hoax number, since the sum of its digits (39) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 11511 + ... + 13209.

It is an arithmetic number, because the mean of its divisors is an integer number (994500).

Almost surely, 2^20999640 is an apocalyptic number.

20999640 is a gapful number since it is divisible by the number (20) 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 20999640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31824000).

20999640 is an abundant number, since it is smaller than the sum of its proper divisors (42648360).

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

20999640 is a wasteful number, since it uses less digits than its factorization.

20999640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1816 (or 1812 counting only the distinct ones).

The product of its (nonzero) digits is 34992, while the sum is 39.

The square root of 20999640 is about 4582.5364155673. The cubic root of 20999640 is about 275.8908411010.

The spelling of 20999640 in words is "twenty million, nine hundred ninety-nine thousand, six hundred forty".