21253720 has 16 divisors (see below), whose sum is σ = 47820960. Its totient is φ = 8501472.

The previous prime is 21253711. The next prime is 21253721. The reversal of 21253720 is 2735212.

It is a super-2 number, since 2×21253720² = 903441227676800, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21253691 and 21253700.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21253721) 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, 265632 + ... + 265711.

It is an arithmetic number, because the mean of its divisors is an integer number (2988810).

Almost surely, 2^21253720 is an apocalyptic number.

21253720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21253720 is an abundant number, since it is smaller than the sum of its proper divisors (26567240).

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

21253720 is a wasteful number, since it uses less digits than its factorization.

21253720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 531354 (or 531350 counting only the distinct ones).

The product of its (nonzero) digits is 840, while the sum is 22.

The square root of 21253720 is about 4610.1757016409. The cubic root of 21253720 is about 276.9990746623. Note that the first 3 decimals are identical.

Adding to 21253720 its reverse (2735212), we get a palindrome (23988932).

The spelling of 21253720 in words is "twenty-one million, two hundred fifty-three thousand, seven hundred twenty".