21005131251 has 8 divisors (see below), whose sum is σ = 30161214160. Its totient is φ = 12926234592.

The previous prime is 21005131247. The next prime is 21005131253. The reversal of 21005131251 is 15213150012.

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

It is not a de Polignac number, because 21005131251 - 2² = 21005131247 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21005131253) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 269296516 + ... + 269296593.

It is an arithmetic number, because the mean of its divisors is an integer number (3770151770).

Almost surely, 2^21005131251 is an apocalyptic number.

21005131251 is a deficient number, since it is larger than the sum of its proper divisors (9156082909).

21005131251 is a wasteful number, since it uses less digits than its factorization.

21005131251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 538593125.

The product of its (nonzero) digits is 300, while the sum is 21.

Adding to 21005131251 its reverse (15213150012), we get a palindrome (36218281263).

The spelling of 21005131251 in words is "twenty-one billion, five million, one hundred thirty-one thousand, two hundred fifty-one".