21251239 has 2 divisors, whose sum is σ = 21251240. Its totient is φ = 21251238.

The previous prime is 21251201. The next prime is 21251257. The reversal of 21251239 is 93215212.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21251239 - 2¹¹ = 21249191 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21251299) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10625619 + 10625620.

It is an arithmetic number, because the mean of its divisors is an integer number (10625620).

Almost surely, 2^21251239 is an apocalyptic number.

21251239 is a deficient number, since it is larger than the sum of its proper divisors (1).

21251239 is an equidigital number, since it uses as much as digits as its factorization.

21251239 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1080, while the sum is 25.

The square root of 21251239 is about 4609.9066151062. The cubic root of 21251239 is about 276.9882959775.

It can be divided in two parts, 2125 and 1239, that added together give a square (3364 = 58²).

The spelling of 21251239 in words is "twenty-one million, two hundred fifty-one thousand, two hundred thirty-nine".