21109993787 has 2 divisors, whose sum is σ = 21109993788. Its totient is φ = 21109993786.

The previous prime is 21109993783. The next prime is 21109993819. The reversal of 21109993787 is 78739990112.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21109993787 - 2² = 21109993783 is a prime.

It is not a weakly prime, because it can be changed into another prime (21109993783) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10554996893 + 10554996894.

It is an arithmetic number, because the mean of its divisors is an integer number (10554996894).

Almost surely, 2^21109993787 is an apocalyptic number.

21109993787 is a deficient number, since it is larger than the sum of its proper divisors (1).

21109993787 is an equidigital number, since it uses as much as digits as its factorization.

21109993787 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1714608, while the sum is 56.

The spelling of 21109993787 in words is "twenty-one billion, one hundred nine million, nine hundred ninety-three thousand, seven hundred eighty-seven".