21042251 has 2 divisors, whose sum is σ = 21042252. Its totient is φ = 21042250.

The previous prime is 21042223. The next prime is 21042283. The reversal of 21042251 is 15224012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21042251 - 2⁶ = 21042187 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21042551) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10521125 + 10521126.

It is an arithmetic number, because the mean of its divisors is an integer number (10521126).

Almost surely, 2^21042251 is an apocalyptic number.

21042251 is a deficient number, since it is larger than the sum of its proper divisors (1).

21042251 is an equidigital number, since it uses as much as digits as its factorization.

21042251 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 160, while the sum is 17.

The square root of 21042251 is about 4587.1833405697. The cubic root of 21042251 is about 276.0773211567.

Adding to 21042251 its reverse (15224012), we get a palindrome (36266263).

The spelling of 21042251 in words is "twenty-one million, forty-two thousand, two hundred fifty-one".