21840397 has 8 divisors (see below), whose sum is σ = 22539776. Its totient is φ = 21146832.

The previous prime is 21840391. The next prime is 21840407. The reversal of 21840397 is 79304812.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21840397 - 2³ = 21840389 is a prime.

It is a super-2 number, since 2×21840397² = 954005882235218, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21840391) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6928 + ... + 9574.

It is an arithmetic number, because the mean of its divisors is an integer number (2817472).

Almost surely, 2^21840397 is an apocalyptic number.

It is an amenable number.

21840397 is a deficient number, since it is larger than the sum of its proper divisors (699379).

21840397 is a wasteful number, since it uses less digits than its factorization.

21840397 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2907.

The product of its (nonzero) digits is 12096, while the sum is 34.

The square root of 21840397 is about 4673.3710531050. The cubic root of 21840397 is about 279.5246910534.

The spelling of 21840397 in words is "twenty-one million, eight hundred forty thousand, three hundred ninety-seven".