21235215251 has 4 divisors (see below), whose sum is σ = 21280687272. Its totient is φ = 21189743232.

The previous prime is 21235215223. The next prime is 21235215259. The reversal of 21235215251 is 15251253212.

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 21235215251 - 2⁶ = 21235215187 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21235215259) 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, 22735310 + ... + 22736243.

It is an arithmetic number, because the mean of its divisors is an integer number (5320171818).

Almost surely, 2^21235215251 is an apocalyptic number.

21235215251 is a deficient number, since it is larger than the sum of its proper divisors (45472021).

21235215251 is an equidigital number, since it uses as much as digits as its factorization.

21235215251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 45472020.

The product of its digits is 6000, while the sum is 29.

Adding to 21235215251 its reverse (15251253212), we get a palindrome (36486468463).

The spelling of 21235215251 in words is "twenty-one billion, two hundred thirty-five million, two hundred fifteen thousand, two hundred fifty-one".