20405540 has 24 divisors (see below), whose sum is σ = 43235640. Its totient is φ = 8089088.

The previous prime is 20405527. The next prime is 20405549. The reversal of 20405540 is 4550402.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 2630884 + 17774656 = 1622^2 + 4216^2 .

It is a Harshad number since it is a multiple of its sum of digits (20).

It is not an unprimeable number, because it can be changed into a prime (20405549) 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, 2255 + ... + 6774.

It is an arithmetic number, because the mean of its divisors is an integer number (1801485).

Almost surely, 2^20405540 is an apocalyptic number.

20405540 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20405540 is an abundant number, since it is smaller than the sum of its proper divisors (22830100).

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

20405540 is a wasteful number, since it uses less digits than its factorization.

20405540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9151 (or 9149 counting only the distinct ones).

The product of its (nonzero) digits is 800, while the sum is 20.

The square root of 20405540 is about 4517.2491629309. The cubic root of 20405540 is about 273.2641737908.

Adding to 20405540 its reverse (4550402), we get a palindrome (24955942).

The spelling of 20405540 in words is "twenty million, four hundred five thousand, five hundred forty".