21131245 has 4 divisors (see below), whose sum is σ = 25357500. Its totient is φ = 16904992.

The previous prime is 21131191. The next prime is 21131251. The reversal of 21131245 is 54213112.

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 2304324 + 18826921 = 1518^2 + 4339^2 .

It is a cyclic number.

It is not a de Polignac number, because 21131245 - 2²³ = 12742637 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2113120 + ... + 2113129.

It is an arithmetic number, because the mean of its divisors is an integer number (6339375).

Almost surely, 2^21131245 is an apocalyptic number.

It is an amenable number.

21131245 is a deficient number, since it is larger than the sum of its proper divisors (4226255).

21131245 is an equidigital number, since it uses as much as digits as its factorization.

21131245 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4226254.

The product of its digits is 240, while the sum is 19.

The square root of 21131245 is about 4596.8733939494. The cubic root of 21131245 is about 276.4659783936.

Adding to 21131245 its reverse (54213112), we get a palindrome (75344357).

The spelling of 21131245 in words is "twenty-one million, one hundred thirty-one thousand, two hundred forty-five".