21243157 has 4 divisors (see below), whose sum is σ = 22877260. Its totient is φ = 19609056.

The previous prime is 21243151. The next prime is 21243181. The reversal of 21243157 is 75134212.

It is a happy number.

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

It can be written as a sum of positive squares in 2 ways, for example, as 13256881 + 7986276 = 3641^2 + 2826^2 .

It is a cyclic number.

It is not a de Polignac number, because 21243157 - 2¹⁵ = 21210389 is a prime.

It is a Duffinian number.

It is a congruent number.

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, 817032 + ... + 817057.

It is an arithmetic number, because the mean of its divisors is an integer number (5719315).

Almost surely, 2^21243157 is an apocalyptic number.

It is an amenable number.

21243157 is a deficient number, since it is larger than the sum of its proper divisors (1634103).

21243157 is a wasteful number, since it uses less digits than its factorization.

21243157 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1634102.

The product of its digits is 1680, while the sum is 25.

The square root of 21243157 is about 4609.0299413217. The cubic root of 21243157 is about 276.9531779740.

Adding to 21243157 its reverse (75134212), we get a palindrome (96377369).

The spelling of 21243157 in words is "twenty-one million, two hundred forty-three thousand, one hundred fifty-seven".