21215249057 has 4 divisors (see below), whose sum is σ = 21215914260. Its totient is φ = 21214583856.

The previous prime is 21215249051. The next prime is 21215249129. The reversal of 21215249057 is 75094251212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 18526204321 + 2689044736 = 136111^2 + 51856^2 .

It is a cyclic number.

It is not a de Polignac number, because 21215249057 - 2⁶ = 21215248993 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21215249057.

It is not an unprimeable number, because it can be changed into a prime (21215249051) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 282218 + ... + 349395.

It is an arithmetic number, because the mean of its divisors is an integer number (5303978565).

Almost surely, 2^21215249057 is an apocalyptic number.

It is an amenable number.

21215249057 is a deficient number, since it is larger than the sum of its proper divisors (665203).

21215249057 is an equidigital number, since it uses as much as digits as its factorization.

21215249057 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 665202.

The product of its (nonzero) digits is 50400, while the sum is 38.

The spelling of 21215249057 in words is "twenty-one billion, two hundred fifteen million, two hundred forty-nine thousand, fifty-seven".