21253440 has 168 divisors, whose sum is σ = 73627488. Its totient is φ = 5191680.

The previous prime is 21253423. The next prime is 21253459. The reversal of 21253440 is 4435212.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 162175 + ... + 162305.

Almost surely, 2^21253440 is an apocalyptic number.

21253440 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 21253440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36813744).

21253440 is an abundant number, since it is smaller than the sum of its proper divisors (52374048).

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

21253440 is a wasteful number, since it uses less digits than its factorization.

21253440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 177 (or 154 counting only the distinct ones).

The product of its (nonzero) digits is 960, while the sum is 21.

The square root of 21253440 is about 4610.1453339347. The cubic root of 21253440 is about 276.9978582465.

Adding to 21253440 its reverse (4435212), we get a palindrome (25688652).

It can be divided in two parts, 2125 and 3440, that added together give a triangular number (5565 = T₁₀₅).

The spelling of 21253440 in words is "twenty-one million, two hundred fifty-three thousand, four hundred forty".