20400640 has 80 divisors (see below), whose sum is σ = 52762248. Its totient is φ = 7520256.

The previous prime is 20400637. The next prime is 20400671. The reversal of 20400640 is 4600402.

It can be written as a sum of positive squares in 4 ways, for example, as 5531904 + 14868736 = 2352^2 + 3856^2 .

It is a tau number, because it is divible by the number of its divisors (80).

It is a super-2 number, since 2×20400640² = 832372224819200, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (16).

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 32974 + ... + 33586.

Almost surely, 2^20400640 is an apocalyptic number.

20400640 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 20400640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26381124).

20400640 is an abundant number, since it is smaller than the sum of its proper divisors (32361608).

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

20400640 is an equidigital number, since it uses as much as digits as its factorization.

20400640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 649 (or 633 counting only the distinct ones).

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

The square root of 20400640 is about 4516.7067648897. The cubic root of 20400640 is about 273.2422989855.

The spelling of 20400640 in words is "twenty million, four hundred thousand, six hundred forty".