20421440 has 56 divisors (see below), whose sum is σ = 52379880. Its totient is φ = 7538688.

The previous prime is 20421433. The next prime is 20421449. The reversal of 20421440 is 4412402.

It can be written as a sum of positive squares in 4 ways, for example, as 4293184 + 16128256 = 2072^2 + 4016^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20421449) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1706 + ... + 6614.

It is an arithmetic number, because the mean of its divisors is an integer number (935355).

Almost surely, 2^20421440 is an apocalyptic number.

20421440 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 20421440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26189940).

20421440 is an abundant number, since it is smaller than the sum of its proper divisors (31958440).

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

20421440 is a wasteful number, since it uses less digits than its factorization.

20421440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4939 (or 4929 counting only the distinct ones).

The product of its (nonzero) digits is 256, while the sum is 17.

The square root of 20421440 is about 4519.0087408634. The cubic root of 20421440 is about 273.3351311931.

Adding to 20421440 its reverse (4412402), we get a palindrome (24833842).

The spelling of 20421440 in words is "twenty million, four hundred twenty-one thousand, four hundred forty".