21097500 has 120 divisors (see below), whose sum is σ = 64291920. Its totient is φ = 5376000.

The previous prime is 21097487. The next prime is 21097513. The reversal of 21097500 is 579012.

It is an interprime number because it is at equal distance from previous prime (21097487) and next prime (21097513).

It is a congruent number.

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 39 ways as a sum of consecutive naturals, for example, 217452 + ... + 217548.

It is an arithmetic number, because the mean of its divisors is an integer number (535766).

Almost surely, 2^21097500 is an apocalyptic number.

21097500 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 21097500, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32145960).

21097500 is an abundant number, since it is smaller than the sum of its proper divisors (43194420).

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

21097500 is a wasteful number, since it uses less digits than its factorization.

21097500 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 153 (or 136 counting only the distinct ones).

The product of its (nonzero) digits is 630, while the sum is 24.

The square root of 21097500 is about 4593.2014978662. The cubic root of 21097500 is about 276.3187349012.

It can be divided in two parts, 2109 and 7500, that multiplied together give a triangular number (15817500 = T₅₆₂₄).

The spelling of 21097500 in words is "twenty-one million, ninety-seven thousand, five hundred".