21002211991 has 2 divisors, whose sum is σ = 21002211992. Its totient is φ = 21002211990.

The previous prime is 21002211983. The next prime is 21002212093. The reversal of 21002211991 is 19911220012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21002211991 - 2³ = 21002211983 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21002211491) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10501105995 + 10501105996.

It is an arithmetic number, because the mean of its divisors is an integer number (10501105996).

Almost surely, 2^21002211991 is an apocalyptic number.

21002211991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21002211991 is an equidigital number, since it uses as much as digits as its factorization.

21002211991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 648, while the sum is 28.

The spelling of 21002211991 in words is "twenty-one billion, two million, two hundred eleven thousand, nine hundred ninety-one".