21312440 has 16 divisors (see below), whose sum is σ = 47953080. Its totient is φ = 8524960.

The previous prime is 21312439. The next prime is 21312449. The reversal of 21312440 is 4421312.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21312449) 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, 266366 + ... + 266445.

Almost surely, 2^21312440 is an apocalyptic number.

21312440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21312440 is an abundant number, since it is smaller than the sum of its proper divisors (26640640).

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

21312440 is a wasteful number, since it uses less digits than its factorization.

21312440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 532822 (or 532818 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 17.

The square root of 21312440 is about 4616.5398297859. The cubic root of 21312440 is about 277.2539387397.

Adding to 21312440 its reverse (4421312), we get a palindrome (25733752).

The spelling of 21312440 in words is "twenty-one million, three hundred twelve thousand, four hundred forty".