21979291 has 4 divisors (see below), whose sum is σ = 22173912. Its totient is φ = 21784672.

The previous prime is 21979289. The next prime is 21979297. The reversal of 21979291 is 19297912.

It is a happy number.

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 21979291 - 2¹ = 21979289 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21979297) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 97141 + ... + 97366.

It is an arithmetic number, because the mean of its divisors is an integer number (5543478).

Almost surely, 2^21979291 is an apocalyptic number.

21979291 is a deficient number, since it is larger than the sum of its proper divisors (194621).

21979291 is a wasteful number, since it uses less digits than its factorization.

21979291 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 194620.

The product of its digits is 20412, while the sum is 40.

The square root of 21979291 is about 4688.2076532509. The cubic root of 21979291 is about 280.1159851118.

The spelling of 21979291 in words is "twenty-one million, nine hundred seventy-nine thousand, two hundred ninety-one".