21321201991 has 2 divisors, whose sum is σ = 21321201992. Its totient is φ = 21321201990.

The previous prime is 21321201989. The next prime is 21321202003. The reversal of 21321201991 is 19910212312.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21321201991 - 2¹ = 21321201989 is a prime.

Together with 21321201989, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21321201971) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10660600995 + 10660600996.

It is an arithmetic number, because the mean of its divisors is an integer number (10660600996).

Almost surely, 2^21321201991 is an apocalyptic number.

21321201991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21321201991 is an equidigital number, since it uses as much as digits as its factorization.

21321201991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1944, while the sum is 31.

The spelling of 21321201991 in words is "twenty-one billion, three hundred twenty-one million, two hundred one thousand, nine hundred ninety-one".