21979999 has 8 divisors (see below), whose sum is σ = 22800960. Its totient is φ = 21163296.

The previous prime is 21979957. The next prime is 21980003. The reversal of 21979999 is 99997912.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21979999 is a prime.

21979999 is a modest number, since divided by 9999 gives 2197 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21979939) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 12609 + ... + 14245.

It is an arithmetic number, because the mean of its divisors is an integer number (2850120).

Almost surely, 2^21979999 is an apocalyptic number.

21979999 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

21979999 is a deficient number, since it is larger than the sum of its proper divisors (820961).

21979999 is a wasteful number, since it uses less digits than its factorization.

21979999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2129.

The product of its digits is 826686, while the sum is 55.

The square root of 21979999 is about 4688.2831612436. The cubic root of 21979999 is about 280.1189927913.

The spelling of 21979999 in words is "twenty-one million, nine hundred seventy-nine thousand, nine hundred ninety-nine".