21243155 has 4 divisors (see below), whose sum is σ = 25491792. Its totient is φ = 16994520.

The previous prime is 21243151. The next prime is 21243181. The reversal of 21243155 is 55134212.

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

It is not a de Polignac number, because 21243155 - 2² = 21243151 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 21243155.

It is not an unprimeable number, because it can be changed into a prime (21243151) 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, 2124311 + ... + 2124320.

It is an arithmetic number, because the mean of its divisors is an integer number (6372948).

Almost surely, 2^21243155 is an apocalyptic number.

21243155 is a deficient number, since it is larger than the sum of its proper divisors (4248637).

21243155 is an equidigital number, since it uses as much as digits as its factorization.

21243155 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4248636.

The product of its digits is 1200, while the sum is 23.

The square root of 21243155 is about 4609.0297243563. The cubic root of 21243155 is about 276.9531692825.

Adding to 21243155 its reverse (55134212), we get a palindrome (76377367).

The spelling of 21243155 in words is "twenty-one million, two hundred forty-three thousand, one hundred fifty-five".