20405640 has 32 divisors (see below), whose sum is σ = 61217280. Its totient is φ = 5441472.

The previous prime is 20405579. The next prime is 20405641. The reversal of 20405640 is 4650402.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20405641) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 84904 + ... + 85143.

It is an arithmetic number, because the mean of its divisors is an integer number (1913040).

Almost surely, 2^20405640 is an apocalyptic number.

20405640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20405640 is an abundant number, since it is smaller than the sum of its proper divisors (40811640).

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

20405640 is a wasteful number, since it uses less digits than its factorization.

20405640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 170061 (or 170057 counting only the distinct ones).

The product of its (nonzero) digits is 960, while the sum is 21.

The square root of 20405640 is about 4517.2602316006. The cubic root of 20405640 is about 273.2646201789.

The spelling of 20405640 in words is "twenty million, four hundred five thousand, six hundred forty".