20991498395887 has 2 divisors, whose sum is σ = 20991498395888. Its totient is φ = 20991498395886.

The previous prime is 20991498395843. The next prime is 20991498395911. The reversal of 20991498395887 is 78859389419902.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20991498395887 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20991498395887.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20391498395887) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10495749197943 + 10495749197944.

It is an arithmetic number, because the mean of its divisors is an integer number (10495749197944).

Almost surely, 2^{20991498395887} is an apocalyptic number.

20991498395887 is a deficient number, since it is larger than the sum of its proper divisors (1).

20991498395887 is an equidigital number, since it uses as much as digits as its factorization.

20991498395887 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2821754880, while the sum is 82.

The spelling of 20991498395887 in words is "twenty trillion, nine hundred ninety-one billion, four hundred ninety-eight million, three hundred ninety-five thousand, eight hundred eighty-seven".