21188207951 has 4 divisors (see below), whose sum is σ = 21196998504. Its totient is φ = 21179417400.

The previous prime is 21188207947. The next prime is 21188208007. The reversal of 21188207951 is 15970288112.

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 21188207951 - 2² = 21188207947 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21188807951) 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, 4391660 + ... + 4396481.

It is an arithmetic number, because the mean of its divisors is an integer number (5299249626).

Almost surely, 2^21188207951 is an apocalyptic number.

21188207951 is a deficient number, since it is larger than the sum of its proper divisors (8790553).

21188207951 is an equidigital number, since it uses as much as digits as its factorization.

21188207951 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8790552.

The product of its (nonzero) digits is 80640, while the sum is 44.

The spelling of 21188207951 in words is "twenty-one billion, one hundred eighty-eight million, two hundred seven thousand, nine hundred fifty-one".