21234440 has 16 divisors (see below), whose sum is σ = 47777580. Its totient is φ = 8493760.

The previous prime is 21234431. The next prime is 21234443. The reversal of 21234440 is 4443212.

It can be written as a sum of positive squares in 2 ways, for example, as 19731364 + 1503076 = 4442^2 + 1226^2 .

It is a super-2 number, since 2×21234440² = 901802884227200, which contains 22 as substring.

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 (21234443) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 265391 + ... + 265470.

Almost surely, 2^21234440 is an apocalyptic number.

21234440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21234440 is an abundant number, since it is smaller than the sum of its proper divisors (26543140).

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

21234440 is a wasteful number, since it uses less digits than its factorization.

21234440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 530872 (or 530868 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 20.

The square root of 21234440 is about 4608.0842006196. The cubic root of 21234440 is about 276.9152907751.

Adding to 21234440 its reverse (4443212), we get a palindrome (25677652).

The spelling of 21234440 in words is "twenty-one million, two hundred thirty-four thousand, four hundred forty".