21156955 has 4 divisors (see below), whose sum is σ = 25388352. Its totient is φ = 16925560.

The previous prime is 21156953. The next prime is 21157039. The reversal of 21156955 is 55965112.

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

It is not a de Polignac number, because 21156955 - 2¹ = 21156953 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 21156955.

It is not an unprimeable number, because it can be changed into a prime (21156953) 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, 2115691 + ... + 2115700.

It is an arithmetic number, because the mean of its divisors is an integer number (6347088).

Almost surely, 2^21156955 is an apocalyptic number.

21156955 is a deficient number, since it is larger than the sum of its proper divisors (4231397).

21156955 is an equidigital number, since it uses as much as digits as its factorization.

21156955 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4231396.

The product of its digits is 13500, while the sum is 34.

The square root of 21156955 is about 4599.6690098310. The cubic root of 21156955 is about 276.5780566542.

The spelling of 21156955 in words is "twenty-one million, one hundred fifty-six thousand, nine hundred fifty-five".