21101099981 has 4 divisors (see below), whose sum is σ = 22724261532. Its totient is φ = 19477938432.

The previous prime is 21101099977. The next prime is 21101099983. The reversal of 21101099981 is 18999010112.

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 4233584356 + 16867515625 = 65066^2 + 129875^2 .

It is a cyclic number.

It is not a de Polignac number, because 21101099981 - 2² = 21101099977 is a prime.

It is a super-2 number, since 2×21101099981² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21101099983) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 811580756 + ... + 811580781.

It is an arithmetic number, because the mean of its divisors is an integer number (5681065383).

Almost surely, 2^21101099981 is an apocalyptic number.

It is an amenable number.

21101099981 is a deficient number, since it is larger than the sum of its proper divisors (1623161551).

21101099981 is a wasteful number, since it uses less digits than its factorization.

21101099981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1623161550.

The product of its (nonzero) digits is 11664, while the sum is 41.

The spelling of 21101099981 in words is "twenty-one billion, one hundred one million, ninety-nine thousand, nine hundred eighty-one".