21497639 has 8 divisors (see below), whose sum is σ = 22808160. Its totient is φ = 20192256.

The previous prime is 21497627. The next prime is 21497657. The reversal of 21497639 is 93679412.

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

It is a cyclic number.

It is not a de Polignac number, because 21497639 - 2²⁰ = 20449063 is a prime.

It is a super-4 number, since 4×21497639⁴ (a number of 30 digits) contains 4444 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21497596 and 21497605.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21497669) 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, 10502 + ... + 12380.

It is an arithmetic number, because the mean of its divisors is an integer number (2851020).

Almost surely, 2^21497639 is an apocalyptic number.

21497639 is a deficient number, since it is larger than the sum of its proper divisors (1310521).

21497639 is a wasteful number, since it uses less digits than its factorization.

21497639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2569.

The product of its digits is 81648, while the sum is 41.

The square root of 21497639 is about 4636.5546475805. The cubic root of 21497639 is about 278.0547094852.

The spelling of 21497639 in words is "twenty-one million, four hundred ninety-seven thousand, six hundred thirty-nine".