20639780 has 36 divisors (see below), whose sum is σ = 50422428. Its totient is φ = 7076160.

The previous prime is 20639779. The next prime is 20639791. The reversal of 20639780 is 8793602.

It can be written as a sum of positive squares in 2 ways, for example, as 15808576 + 4831204 = 3976^2 + 2198^2 .

It is a Harshad number since it is a multiple of its sum of digits (35).

It is a self number, because there is not a number n which added to its sum of digits gives 20639780.

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 11 ways as a sum of consecutive naturals, for example, 9551 + ... + 11510.

It is an arithmetic number, because the mean of its divisors is an integer number (1400623).

Almost surely, 2^20639780 is an apocalyptic number.

20639780 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20639780 is an abundant number, since it is smaller than the sum of its proper divisors (29782648).

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

20639780 is a wasteful number, since it uses less digits than its factorization.

20639780 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21084 (or 21075 counting only the distinct ones).

The product of its (nonzero) digits is 18144, while the sum is 35.

The square root of 20639780 is about 4543.1024641758. The cubic root of 20639780 is about 274.3058194071.

The spelling of 20639780 in words is "twenty million, six hundred thirty-nine thousand, seven hundred eighty".