21689957 has 4 divisors (see below), whose sum is σ = 21702156. Its totient is φ = 21677760.

The previous prime is 21689947. The next prime is 21689959. The reversal of 21689957 is 75998612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 10407076 + 11282881 = 3226^2 + 3359^2 .

It is a cyclic number.

It is not a de Polignac number, because 21689957 - 2⁶ = 21689893 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21689959) 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, 2858 + ... + 7179.

It is an arithmetic number, because the mean of its divisors is an integer number (5425539).

Almost surely, 2^21689957 is an apocalyptic number.

It is an amenable number.

21689957 is a deficient number, since it is larger than the sum of its proper divisors (12199).

21689957 is a wasteful number, since it uses less digits than its factorization.

21689957 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12198.

The product of its digits is 272160, while the sum is 47.

The square root of 21689957 is about 4657.2477924199. The cubic root of 21689957 is about 278.8814088129.

The spelling of 21689957 in words is "twenty-one million, six hundred eighty-nine thousand, nine hundred fifty-seven".