21099979 has 4 divisors (see below), whose sum is σ = 21141000. Its totient is φ = 21058960.

The previous prime is 21099977. The next prime is 21100003. The reversal of 21099979 is 97999012.

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

It is a cyclic number.

It is not a de Polignac number, because 21099979 - 2¹ = 21099977 is a prime.

It is a super-2 number, since 2×21099979² = 890418227600882, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21099973) 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, 19729 + ... + 20770.

It is an arithmetic number, because the mean of its divisors is an integer number (5285250).

Almost surely, 2^21099979 is an apocalyptic number.

21099979 is a deficient number, since it is larger than the sum of its proper divisors (41021).

21099979 is an equidigital number, since it uses as much as digits as its factorization.

21099979 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 41020.

The product of its (nonzero) digits is 91854, while the sum is 46.

The square root of 21099979 is about 4593.4713452900. The cubic root of 21099979 is about 276.3295571521.

The spelling of 21099979 in words is "twenty-one million, ninety-nine thousand, nine hundred seventy-nine".