21105251 has 4 divisors (see below), whose sum is σ = 21164400. Its totient is φ = 21046104.

The previous prime is 21105239. The next prime is 21105307. The reversal of 21105251 is 15250112.

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 21105251 - 2⁶ = 21105187 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21105221) 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, 29036 + ... + 29753.

It is an arithmetic number, because the mean of its divisors is an integer number (5291100).

Almost surely, 2^21105251 is an apocalyptic number.

21105251 is a deficient number, since it is larger than the sum of its proper divisors (59149).

21105251 is an equidigital number, since it uses as much as digits as its factorization.

21105251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 59148.

The product of its (nonzero) digits is 100, while the sum is 17.

The square root of 21105251 is about 4594.0451673879. The cubic root of 21105251 is about 276.3525696254.

Adding to 21105251 its reverse (15250112), we get a palindrome (36355363).

The spelling of 21105251 in words is "twenty-one million, one hundred five thousand, two hundred fifty-one".