21057000251 has 12 divisors (see below), whose sum is σ = 24737407200. Its totient is φ = 17870151600.

The previous prime is 21057000247. The next prime is 21057000271. The reversal of 21057000251 is 15200075012.

It is a happy number.

It is not a de Polignac number, because 21057000251 - 2² = 21057000247 is a prime.

It is a super-2 number, since 2×21057000251² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21057000271) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2122451 + ... + 2132348.

It is an arithmetic number, because the mean of its divisors is an integer number (2061450600).

Almost surely, 2^21057000251 is an apocalyptic number.

21057000251 is a deficient number, since it is larger than the sum of its proper divisors (3680406949).

21057000251 is a wasteful number, since it uses less digits than its factorization.

21057000251 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4254914 (or 4254907 counting only the distinct ones).

The product of its (nonzero) digits is 700, while the sum is 23.

Adding to 21057000251 its reverse (15200075012), we get a palindrome (36257075263).

The spelling of 21057000251 in words is "twenty-one billion, fifty-seven million, two hundred fifty-one", and thus it is an aban number.