21100091921 has 4 divisors (see below), whose sum is σ = 21116616372. Its totient is φ = 21083567472.

The previous prime is 21100091911. The next prime is 21100091941. The reversal of 21100091921 is 12919000112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 16831429696 + 4268662225 = 129736^2 + 65335^2 .

It is a cyclic number.

It is not a de Polignac number, because 21100091921 - 2¹⁴ = 21100075537 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21100091911) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8260310 + ... + 8262863.

It is an arithmetic number, because the mean of its divisors is an integer number (5279154093).

Almost surely, 2^21100091921 is an apocalyptic number.

It is an amenable number.

21100091921 is a deficient number, since it is larger than the sum of its proper divisors (16524451).

21100091921 is a wasteful number, since it uses less digits than its factorization.

21100091921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16524450.

The product of its (nonzero) digits is 324, while the sum is 26.

The spelling of 21100091921 in words is "twenty-one billion, one hundred million, ninety-one thousand, nine hundred twenty-one".