21121021991 has 2 divisors, whose sum is σ = 21121021992. Its totient is φ = 21121021990.

The previous prime is 21121021939. The next prime is 21121022017. The reversal of 21121021991 is 19912012112.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21121021991 - 2²² = 21116827687 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21121023991) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10560510995 + 10560510996.

It is an arithmetic number, because the mean of its divisors is an integer number (10560510996).

Almost surely, 2^21121021991 is an apocalyptic number.

21121021991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21121021991 is an equidigital number, since it uses as much as digits as its factorization.

21121021991 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 29.

The spelling of 21121021991 in words is "twenty-one billion, one hundred twenty-one million, twenty-one thousand, nine hundred ninety-one".