21247943991 has 4 divisors (see below), whose sum is σ = 28330591992. Its totient is φ = 14165295992.

The previous prime is 21247943971. The next prime is 21247944001. The reversal of 21247943991 is 19934974212.

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

It is a cyclic number.

It is not a de Polignac number, because 21247943991 - 2¹⁰ = 21247942967 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21247943971) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3541323996 + ... + 3541324001.

It is an arithmetic number, because the mean of its divisors is an integer number (7082647998).

Almost surely, 2^21247943991 is an apocalyptic number.

21247943991 is a deficient number, since it is larger than the sum of its proper divisors (7082648001).

21247943991 is an equidigital number, since it uses as much as digits as its factorization.

21247943991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7082648000.

The product of its digits is 979776, while the sum is 51.

The spelling of 21247943991 in words is "twenty-one billion, two hundred forty-seven million, nine hundred forty-three thousand, nine hundred ninety-one".