21297540 has 144 divisors (see below), whose sum is σ = 69120576. Its totient is φ = 4857600.

The previous prime is 21297539. The next prime is 21297541. The reversal of 21297540 is 4579212.

It is an interprime number because it is at equal distance from previous prime (21297539) and next prime (21297541).

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 21297498 and 21297507.

It is not an unprimeable number, because it can be changed into a prime (21297541) by changing a digit.

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 47 ways as a sum of consecutive naturals, for example, 349110 + ... + 349170.

It is an arithmetic number, because the mean of its divisors is an integer number (480004).

Almost surely, 2^21297540 is an apocalyptic number.

21297540 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 21297540, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34560288).

21297540 is an abundant number, since it is smaller than the sum of its proper divisors (47823036).

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

21297540 is a wasteful number, since it uses less digits than its factorization.

21297540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 130 (or 105 counting only the distinct ones).

The product of its (nonzero) digits is 5040, while the sum is 30.

The square root of 21297540 is about 4614.9257848854. The cubic root of 21297540 is about 277.1893122153.

It can be divided in two parts, 2129 and 7540, that added together give a palindrome (9669).

The spelling of 21297540 in words is "twenty-one million, two hundred ninety-seven thousand, five hundred forty".