21129655 has 4 divisors (see below), whose sum is σ = 25355592. Its totient is φ = 16903720.

The previous prime is 21129643. The next prime is 21129673. The reversal of 21129655 is 55692112.

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

It is not a de Polignac number, because 21129655 - 2¹¹ = 21127607 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 2112961 + ... + 2112970.

It is an arithmetic number, because the mean of its divisors is an integer number (6338898).

Almost surely, 2^21129655 is an apocalyptic number.

21129655 is a deficient number, since it is larger than the sum of its proper divisors (4225937).

21129655 is an equidigital number, since it uses as much as digits as its factorization.

21129655 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4225936.

The product of its digits is 5400, while the sum is 31.

The square root of 21129655 is about 4596.7004470598. The cubic root of 21129655 is about 276.4590440817.

The spelling of 21129655 in words is "twenty-one million, one hundred twenty-nine thousand, six hundred fifty-five".