21220312991 has 2 divisors, whose sum is σ = 21220312992. Its totient is φ = 21220312990.

The previous prime is 21220312979. The next prime is 21220313021. The reversal of 21220312991 is 19921302212.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21220312991 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21220312901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10610156495 + 10610156496.

It is an arithmetic number, because the mean of its divisors is an integer number (10610156496).

Almost surely, 2^21220312991 is an apocalyptic number.

21220312991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21220312991 is an equidigital number, since it uses as much as digits as its factorization.

21220312991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3888, while the sum is 32.

The spelling of 21220312991 in words is "twenty-one billion, two hundred twenty million, three hundred twelve thousand, nine hundred ninety-one".