21113178991 has 2 divisors, whose sum is σ = 21113178992. Its totient is φ = 21113178990.

The previous prime is 21113178943. The next prime is 21113178997. The reversal of 21113178991 is 19987131112.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21113178991 - 2¹⁷ = 21113047919 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21113178997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10556589495 + 10556589496.

It is an arithmetic number, because the mean of its divisors is an integer number (10556589496).

Almost surely, 2^21113178991 is an apocalyptic number.

21113178991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21113178991 is an equidigital number, since it uses as much as digits as its factorization.

21113178991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 27216, while the sum is 43.

The spelling of 21113178991 in words is "twenty-one billion, one hundred thirteen million, one hundred seventy-eight thousand, nine hundred ninety-one".