21979121 has 2 divisors, whose sum is σ = 21979122. Its totient is φ = 21979120.

The previous prime is 21979117. The next prime is 21979151. The reversal of 21979121 is 12197912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13359025 + 8620096 = 3655^2 + 2936^2 .

It is a cyclic number.

It is not a de Polignac number, because 21979121 - 2² = 21979117 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21979151) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10989560 + 10989561.

It is an arithmetic number, because the mean of its divisors is an integer number (10989561).

Almost surely, 2^21979121 is an apocalyptic number.

It is an amenable number.

21979121 is a deficient number, since it is larger than the sum of its proper divisors (1).

21979121 is an equidigital number, since it uses as much as digits as its factorization.

21979121 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2268, while the sum is 32.

The square root of 21979121 is about 4688.1895226196. The cubic root of 21979121 is about 280.1152629193.

The spelling of 21979121 in words is "twenty-one million, nine hundred seventy-nine thousand, one hundred twenty-one".