21420001243 has 4 divisors (see below), whose sum is σ = 21427969720. Its totient is φ = 21412032768.

The previous prime is 21420001181. The next prime is 21420001247. The reversal of 21420001243 is 34210002412.

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-21420001243 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 21420001243.

It is not an unprimeable number, because it can be changed into a prime (21420001247) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3980205 + ... + 3985582.

It is an arithmetic number, because the mean of its divisors is an integer number (5356992430).

Almost surely, 2^21420001243 is an apocalyptic number.

21420001243 is a deficient number, since it is larger than the sum of its proper divisors (7968477).

21420001243 is an equidigital number, since it uses as much as digits as its factorization.

21420001243 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7968476.

The product of its (nonzero) digits is 384, while the sum is 19.

Adding to 21420001243 its reverse (34210002412), we get a palindrome (55630003655).

The spelling of 21420001243 in words is "twenty-one billion, four hundred twenty million, one thousand, two hundred forty-three".