21979421 has 6 divisors (see below), whose sum is σ = 22977150. Its totient is φ = 21023288.

The previous prime is 21979387. The next prime is 21979423. The reversal of 21979421 is 12497912.

It can be written as a sum of positive squares in only one way, i.e., 13039321 + 8940100 = 3611^2 + 2990^2 .

It is not a de Polignac number, because 21979421 - 2⁶ = 21979357 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21979423) 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 5 ways as a sum of consecutive naturals, for example, 20246 + ... + 21303.

It is an arithmetic number, because the mean of its divisors is an integer number (3829525).

Almost surely, 2^21979421 is an apocalyptic number.

It is an amenable number.

21979421 is a deficient number, since it is larger than the sum of its proper divisors (997729).

21979421 is an equidigital number, since it uses as much as digits as its factorization.

21979421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41595 (or 41572 counting only the distinct ones).

The product of its digits is 9072, while the sum is 35.

The square root of 21979421 is about 4688.2215178040. The cubic root of 21979421 is about 280.1165373742.

The spelling of 21979421 in words is "twenty-one million, nine hundred seventy-nine thousand, four hundred twenty-one".