21253240 has 16 divisors (see below), whose sum is σ = 47819880. Its totient is φ = 8501280.

The previous prime is 21253237. The next prime is 21253241. The reversal of 21253240 is 4235212.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21253241) 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, 265626 + ... + 265705.

Almost surely, 2^21253240 is an apocalyptic number.

21253240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21253240 is an abundant number, since it is smaller than the sum of its proper divisors (26566640).

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

21253240 is a wasteful number, since it uses less digits than its factorization.

21253240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 531342 (or 531338 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 19.

The square root of 21253240 is about 4610.1236425935. The cubic root of 21253240 is about 276.9969893715.

Adding to 21253240 its reverse (4235212), we get a palindrome (25488452).

The spelling of 21253240 in words is "twenty-one million, two hundred fifty-three thousand, two hundred forty".