21010009991 has 2 divisors, whose sum is σ = 21010009992. Its totient is φ = 21010009990.

The previous prime is 21010009957. The next prime is 21010010011. The reversal of 21010009991 is 19990001012.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21010009991 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21010009901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10505004995 + 10505004996.

It is an arithmetic number, because the mean of its divisors is an integer number (10505004996).

Almost surely, 2^21010009991 is an apocalyptic number.

21010009991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21010009991 is an equidigital number, since it uses as much as digits as its factorization.

21010009991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1458, while the sum is 32.

The spelling of 21010009991 in words is "twenty-one billion, ten million, nine thousand, nine hundred ninety-one".