21253540 has 96 divisors (see below), whose sum is σ = 57302784. Its totient is φ = 6428160.

The previous prime is 21253537. The next prime is 21253543. The reversal of 21253540 is 4535212.

It is an interprime number because it is at equal distance from previous prime (21253537) and next prime (21253543).

It is a Harshad number since it is a multiple of its sum of digits (22).

It is not an unprimeable number, because it can be changed into a prime (21253543) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 56794 + ... + 57166.

It is an arithmetic number, because the mean of its divisors is an integer number (596904).

Almost surely, 2^21253540 is an apocalyptic number.

21253540 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 21253540, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28651392).

21253540 is an abundant number, since it is smaller than the sum of its proper divisors (36049244).

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

21253540 is a wasteful number, since it uses less digits than its factorization.

21253540 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 437 (or 435 counting only the distinct ones).

The product of its (nonzero) digits is 1200, while the sum is 22.

The square root of 21253540 is about 4610.1561795670. The cubic root of 21253540 is about 276.9982926819.

Adding to 21253540 its reverse (4535212), we get a palindrome (25788752).

It can be divided in two parts, 2125 and 3540, that added together give a palindrome (5665).

The spelling of 21253540 in words is "twenty-one million, two hundred fifty-three thousand, five hundred forty".