21253740 has 96 divisors (see below), whose sum is σ = 64157184. Its totient is φ = 5237760.

The previous prime is 21253721. The next prime is 21253759. The reversal of 21253740 is 4735212.

It is an interprime number because it is at equal distance from previous prime (21253721) and next prime (21253759).

It is a self number, because there is not a number n which added to its sum of digits gives 21253740.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 68185 + ... + 68495.

It is an arithmetic number, because the mean of its divisors is an integer number (668304).

Almost surely, 2^21253740 is an apocalyptic number.

21253740 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 21253740, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32078592).

21253740 is an abundant number, since it is smaller than the sum of its proper divisors (42903444).

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

21253740 is a wasteful number, since it uses less digits than its factorization.

21253740 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 407 (or 405 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 24.

The square root of 21253740 is about 4610.1778707551. The cubic root of 21253740 is about 276.9991615487. Note that the first 3 decimals are identical.

Adding to 21253740 its reverse (4735212), we get a palindrome (25988952).

The spelling of 21253740 in words is "twenty-one million, two hundred fifty-three thousand, seven hundred forty".