21809155 has 8 divisors (see below), whose sum is σ = 26205984. Its totient is φ = 17424000.

The previous prime is 21809153. The next prime is 21809159. The reversal of 21809155 is 55190812.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21809155 - 2¹ = 21809153 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21809153) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1930 + ... + 6880.

It is an arithmetic number, because the mean of its divisors is an integer number (3275748).

Almost surely, 2^21809155 is an apocalyptic number.

21809155 is a deficient number, since it is larger than the sum of its proper divisors (4396829).

21809155 is an equidigital number, since it uses as much as digits as its factorization.

21809155 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5837.

The product of its (nonzero) digits is 3600, while the sum is 31.

The square root of 21809155 is about 4670.0273018474. The cubic root of 21809155 is about 279.3913436947.

Adding to 21809155 its reverse (55190812), we get a palindrome (76999967).

The spelling of 21809155 in words is "twenty-one million, eight hundred nine thousand, one hundred fifty-five".