21351251 has 4 divisors (see below), whose sum is σ = 21621600. Its totient is φ = 21080904.

The previous prime is 21351241. The next prime is 21351287. The reversal of 21351251 is 15215312.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21351251 - 2¹⁴ = 21334867 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21351241) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 135056 + ... + 135213.

It is an arithmetic number, because the mean of its divisors is an integer number (5405400).

Almost surely, 2^21351251 is an apocalyptic number.

21351251 is a deficient number, since it is larger than the sum of its proper divisors (270349).

21351251 is an equidigital number, since it uses as much as digits as its factorization.

21351251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 270348.

The product of its digits is 300, while the sum is 20.

The square root of 21351251 is about 4620.7413907294. The cubic root of 21351251 is about 277.4221343635.

Adding to 21351251 its reverse (15215312), we get a palindrome (36566563).

The spelling of 21351251 in words is "twenty-one million, three hundred fifty-one thousand, two hundred fifty-one".