20391840 has 324 divisors, whose sum is σ = 85990086. Its totient is φ = 4386816.

The previous prime is 20391821. The next prime is 20391841. The reversal of 20391840 is 4819302.

It can be written as a sum of positive squares in 3 ways, for example, as 19820304 + 571536 = 4452^2 + 756^2 .

It is not an unprimeable number, because it can be changed into a prime (20391841) by changing a digit.

It is a polite number, since it can be written in 53 ways as a sum of consecutive naturals, for example, 1199512 + ... + 1199528.

Almost surely, 2^20391840 is an apocalyptic number.

20391840 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 20391840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (42995043).

20391840 is an abundant number, since it is smaller than the sum of its proper divisors (65598246).

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

20391840 is a wasteful number, since it uses less digits than its factorization.

20391840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 69 (or 34 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 20391840 is about 4515.7324987204. The cubic root of 20391840 is about 273.2030048252.

The spelling of 20391840 in words is "twenty million, three hundred ninety-one thousand, eight hundred forty".