21689537 has 4 divisors (see below), whose sum is σ = 21704496. Its totient is φ = 21674580.

The previous prime is 21689531. The next prime is 21689543. The reversal of 21689537 is 73598612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is an interprime number because it is at equal distance from previous prime (21689531) and next prime (21689543).

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21689537 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21689494 and 21689503.

It is not an unprimeable number, because it can be changed into a prime (21689531) 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, 5039 + ... + 8292.

It is an arithmetic number, because the mean of its divisors is an integer number (5426124).

Almost surely, 2^21689537 is an apocalyptic number.

It is an amenable number.

21689537 is a deficient number, since it is larger than the sum of its proper divisors (14959).

21689537 is a wasteful number, since it uses less digits than its factorization.

21689537 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14958.

The product of its digits is 90720, while the sum is 41.

The square root of 21689537 is about 4657.2027011931. The cubic root of 21689537 is about 278.8796087333.

The spelling of 21689537 in words is "twenty-one million, six hundred eighty-nine thousand, five hundred thirty-seven".