21001030991 has 2 divisors, whose sum is σ = 21001030992. Its totient is φ = 21001030990.

The previous prime is 21001030979. The next prime is 21001030993. The reversal of 21001030991 is 19903010012.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21001030991 - 2¹⁰ = 21001029967 is a prime.

Together with 21001030993, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21001030991.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21001030993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500515495 + 10500515496.

It is an arithmetic number, because the mean of its divisors is an integer number (10500515496).

Almost surely, 2^21001030991 is an apocalyptic number.

21001030991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21001030991 is an equidigital number, since it uses as much as digits as its factorization.

21001030991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 486, while the sum is 26.

The spelling of 21001030991 in words is "twenty-one billion, one million, thirty thousand, nine hundred ninety-one".