21330021991 has 2 divisors, whose sum is σ = 21330021992. Its totient is φ = 21330021990.

The previous prime is 21330021959. The next prime is 21330022013. The reversal of 21330021991 is 19912003312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21330021991 - 2⁵ = 21330021959 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21330021191) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10665010995 + 10665010996.

It is an arithmetic number, because the mean of its divisors is an integer number (10665010996).

Almost surely, 2^21330021991 is an apocalyptic number.

21330021991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21330021991 is an equidigital number, since it uses as much as digits as its factorization.

21330021991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2916, while the sum is 31.

The spelling of 21330021991 in words is "twenty-one billion, three hundred thirty million, twenty-one thousand, nine hundred ninety-one".