21121099991 has 2 divisors, whose sum is σ = 21121099992. Its totient is φ = 21121099990.

The previous prime is 21121099973. The next prime is 21121100047. The reversal of 21121099991 is 19999012112.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21121099991 - 2¹⁸ = 21120837847 is a prime.

It is a super-3 number, since 3×21121099991³ (a number of 32 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21121099921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10560549995 + 10560549996.

It is an arithmetic number, because the mean of its divisors is an integer number (10560549996).

Almost surely, 2^21121099991 is an apocalyptic number.

21121099991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21121099991 is an equidigital number, since it uses as much as digits as its factorization.

21121099991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 26244, while the sum is 44.

The spelling of 21121099991 in words is "twenty-one billion, one hundred twenty-one million, ninety-nine thousand, nine hundred ninety-one".