21097840 has 20 divisors (see below), whose sum is σ = 49052664. Its totient is φ = 8439104.

The previous prime is 21097823. The next prime is 21097841. The reversal of 21097840 is 4879012.

It is a tau number, because it is divible by the number of its divisors (20).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21097841) 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, 131782 + ... + 131941.

Almost surely, 2^21097840 is an apocalyptic number.

21097840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21097840 is an abundant number, since it is smaller than the sum of its proper divisors (27954824).

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

21097840 is a wasteful number, since it uses less digits than its factorization.

21097840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 263736 (or 263730 counting only the distinct ones).

The product of its (nonzero) digits is 4032, while the sum is 31.

The square root of 21097840 is about 4593.2385089390. The cubic root of 21097840 is about 276.3202192455.

The spelling of 21097840 in words is "twenty-one million, ninety-seven thousand, eight hundred forty".