21215440243 has 4 divisors (see below), whose sum is σ = 21282366240. Its totient is φ = 21148514248.

The previous prime is 21215440231. The next prime is 21215440307. The reversal of 21215440243 is 34204451212.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21215440243 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21215449243) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 33462523 + ... + 33463156.

It is an arithmetic number, because the mean of its divisors is an integer number (5320591560).

Almost surely, 2^21215440243 is an apocalyptic number.

21215440243 is a deficient number, since it is larger than the sum of its proper divisors (66925997).

21215440243 is an equidigital number, since it uses as much as digits as its factorization.

21215440243 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 66925996.

The product of its (nonzero) digits is 7680, while the sum is 28.

Adding to 21215440243 its reverse (34204451212), we get a palindrome (55419891455).

The spelling of 21215440243 in words is "twenty-one billion, two hundred fifteen million, four hundred forty thousand, two hundred forty-three".