21156211691 has 2 divisors, whose sum is σ = 21156211692. Its totient is φ = 21156211690.

The previous prime is 21156211679. The next prime is 21156211717. The reversal of 21156211691 is 19611265112.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21156211691 - 2¹⁰ = 21156210667 is a prime.

It is a super-2 number, since 2×21156211691² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21156211621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10578105845 + 10578105846.

It is an arithmetic number, because the mean of its divisors is an integer number (10578105846).

Almost surely, 2^21156211691 is an apocalyptic number.

21156211691 is a deficient number, since it is larger than the sum of its proper divisors (1).

21156211691 is an equidigital number, since it uses as much as digits as its factorization.

21156211691 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6480, while the sum is 35.

The spelling of 21156211691 in words is "twenty-one billion, one hundred fifty-six million, two hundred eleven thousand, six hundred ninety-one".