20640040 has 64 divisors (see below), whose sum is σ = 49766400. Its totient is φ = 7676928.

The previous prime is 20640019. The next prime is 20640047. The reversal of 20640040 is 4004602.

It is a super-2 number, since 2×20640040² = 852022502403200, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 20639996 and 20640023.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20640047) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 86241 + ... + 86479.

It is an arithmetic number, because the mean of its divisors is an integer number (777600).

Almost surely, 2^20640040 is an apocalyptic number.

20640040 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 20640040, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24883200).

20640040 is an abundant number, since it is smaller than the sum of its proper divisors (29126360).

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

20640040 is a wasteful number, since it uses less digits than its factorization.

20640040 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 394 (or 390 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 16.

The square root of 20640040 is about 4543.1310788926. The cubic root of 20640040 is about 274.3069712155.

Adding to 20640040 its reverse (4004602), we get a palindrome (24644642).

The spelling of 20640040 in words is "twenty million, six hundred forty thousand, forty".