21808155 has 8 divisors (see below), whose sum is σ = 34893072. Its totient is φ = 11631008.

The previous prime is 21808153. The next prime is 21808177. The reversal of 21808155 is 55180812.

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 21808155 - 2¹ = 21808153 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21808153) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 726924 + ... + 726953.

It is an arithmetic number, because the mean of its divisors is an integer number (4361634).

Almost surely, 2^21808155 is an apocalyptic number.

21808155 is a deficient number, since it is larger than the sum of its proper divisors (13084917).

21808155 is a wasteful number, since it uses less digits than its factorization.

21808155 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1453885.

The product of its (nonzero) digits is 3200, while the sum is 30.

The square root of 21808155 is about 4669.9202348648. The cubic root of 21808155 is about 279.3870733838.

Adding to 21808155 its reverse (55180812), we get a palindrome (76988967).

The spelling of 21808155 in words is "twenty-one million, eight hundred eight thousand, one hundred fifty-five".