21938479921 has 2 divisors, whose sum is σ = 21938479922. Its totient is φ = 21938479920.

The previous prime is 21938479909. The next prime is 21938479951. The reversal of 21938479921 is 12997483912.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13773369600 + 8165110321 = 117360^2 + 90361^2 .

It is a cyclic number.

It is not a de Polignac number, because 21938479921 - 2²⁵ = 21904925489 is a prime.

It is not a weakly prime, because it can be changed into another prime (21938479951) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10969239960 + 10969239961.

It is an arithmetic number, because the mean of its divisors is an integer number (10969239961).

Almost surely, 2^21938479921 is an apocalyptic number.

It is an amenable number.

21938479921 is a deficient number, since it is larger than the sum of its proper divisors (1).

21938479921 is an equidigital number, since it uses as much as digits as its factorization.

21938479921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1959552, while the sum is 55.

The spelling of 21938479921 in words is "twenty-one billion, nine hundred thirty-eight million, four hundred seventy-nine thousand, nine hundred twenty-one".