21000123251 has 8 divisors (see below), whose sum is σ = 22379410944. Its totient is φ = 19659688840.

The previous prime is 21000123241. The next prime is 21000123257. The reversal of 21000123251 is 15232100012.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21000123251 - 2⁶ = 21000123187 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21000123257) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9712205 + ... + 9714366.

It is an arithmetic number, because the mean of its divisors is an integer number (2797426368).

Almost surely, 2^21000123251 is an apocalyptic number.

21000123251 is a deficient number, since it is larger than the sum of its proper divisors (1379287693).

21000123251 is a wasteful number, since it uses less digits than its factorization.

21000123251 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19426641.

The product of its (nonzero) digits is 120, while the sum is 17.

Adding to 21000123251 its reverse (15232100012), we get a palindrome (36232223263).

The spelling of 21000123251 in words is "twenty-one billion, one hundred twenty-three thousand, two hundred fifty-one".