21689955 has 48 divisors (see below), whose sum is σ = 44151744. Its totient is φ = 9642240.

The previous prime is 21689947. The next prime is 21689959. The reversal of 21689955 is 55998612.

It is not a de Polignac number, because 21689955 - 2³ = 21689947 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a self number, because there is not a number n which added to its sum of digits gives 21689955.

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 47 ways as a sum of consecutive naturals, for example, 10725 + ... + 12585.

It is an arithmetic number, because the mean of its divisors is an integer number (919828).

Almost surely, 2^21689955 is an apocalyptic number.

21689955 is an abundant number, since it is smaller than the sum of its proper divisors (22461789).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21689955 is a wasteful number, since it uses less digits than its factorization.

21689955 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1916 (or 1913 counting only the distinct ones).

The product of its digits is 194400, while the sum is 45.

The square root of 21689955 is about 4657.2475777008. The cubic root of 21689955 is about 278.8814002411.

The spelling of 21689955 in words is "twenty-one million, six hundred eighty-nine thousand, nine hundred fifty-five".