21687121 has 8 divisors (see below), whose sum is σ = 23103360. Its totient is φ = 20286528.

The previous prime is 21687119. The next prime is 21687191. The reversal of 21687121 is 12178612.

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 21687121 - 2¹ = 21687119 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21687121.

It is not an unprimeable number, because it can be changed into a prime (21687101) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 981 + ... + 6658.

It is an arithmetic number, because the mean of its divisors is an integer number (2887920).

Almost surely, 2^21687121 is an apocalyptic number.

It is an amenable number.

21687121 is a deficient number, since it is larger than the sum of its proper divisors (1416239).

21687121 is a wasteful number, since it uses less digits than its factorization.

21687121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7823.

The product of its digits is 1344, while the sum is 28.

The square root of 21687121 is about 4656.9433107995. The cubic root of 21687121 is about 278.8692535383.

The spelling of 21687121 in words is "twenty-one million, six hundred eighty-seven thousand, one hundred twenty-one".