21156772811 has 4 divisors (see below), whose sum is σ = 21157090824. Its totient is φ = 21156454800.

The previous prime is 21156772807. The next prime is 21156772831. The reversal of 21156772811 is 11827765112.

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 21156772811 - 2² = 21156772807 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21156772831) 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, 16850 + ... + 206391.

It is an arithmetic number, because the mean of its divisors is an integer number (5289272706).

Almost surely, 2^21156772811 is an apocalyptic number.

21156772811 is a deficient number, since it is larger than the sum of its proper divisors (318013).

21156772811 is an equidigital number, since it uses as much as digits as its factorization.

21156772811 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 318012.

The product of its digits is 47040, while the sum is 41.

The spelling of 21156772811 in words is "twenty-one billion, one hundred fifty-six million, seven hundred seventy-two thousand, eight hundred eleven".