21979289 has 2 divisors, whose sum is σ = 21979290. Its totient is φ = 21979288.

The previous prime is 21979267. The next prime is 21979297. The reversal of 21979289 is 98297912.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12369289 + 9610000 = 3517^2 + 3100^2 .

It is a cyclic number.

It is not a de Polignac number, because 21979289 - 2²⁴ = 5202073 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21979229) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10989644 + 10989645.

It is an arithmetic number, because the mean of its divisors is an integer number (10989645).

Almost surely, 2^21979289 is an apocalyptic number.

It is an amenable number.

21979289 is a deficient number, since it is larger than the sum of its proper divisors (1).

21979289 is an equidigital number, since it uses as much as digits as its factorization.

21979289 is an evil number, because the sum of its binary digits is even.

The product of its digits is 163296, while the sum is 47.

The square root of 21979289 is about 4688.2074399497. The cubic root of 21979289 is about 280.1159766155.

The spelling of 21979289 in words is "twenty-one million, nine hundred seventy-nine thousand, two hundred eighty-nine".