21311020391 has 2 divisors, whose sum is σ = 21311020392. Its totient is φ = 21311020390.

The previous prime is 21311020343. The next prime is 21311020403. The reversal of 21311020391 is 19302011312.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21311020391 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21311028391) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10655510195 + 10655510196.

It is an arithmetic number, because the mean of its divisors is an integer number (10655510196).

Almost surely, 2^21311020391 is an apocalyptic number.

21311020391 is a deficient number, since it is larger than the sum of its proper divisors (1).

21311020391 is an equidigital number, since it uses as much as digits as its factorization.

21311020391 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 324, while the sum is 23.

The spelling of 21311020391 in words is "twenty-one billion, three hundred eleven million, twenty thousand, three hundred ninety-one".