21920121 has 6 divisors (see below), whose sum is σ = 31662410. Its totient is φ = 14613408.

The previous prime is 21920113. The next prime is 21920141. The reversal of 21920121 is 12102912.

It can be written as a sum of positive squares in only one way, i.e., 11128896 + 10791225 = 3336^2 + 3285^2 .

It is not a de Polignac number, because 21920121 - 2³ = 21920113 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21920094 and 21920103.

It is not an unprimeable number, because it can be changed into a prime (21920141) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1217776 + ... + 1217793.

Almost surely, 2^21920121 is an apocalyptic number.

It is an amenable number.

21920121 is a deficient number, since it is larger than the sum of its proper divisors (9742289).

21920121 is a wasteful number, since it uses less digits than its factorization.

21920121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2435575 (or 2435572 counting only the distinct ones).

The product of its (nonzero) digits is 72, while the sum is 18.

The square root of 21920121 is about 4681.8928864296. The cubic root of 21920121 is about 279.8643943700.

The spelling of 21920121 in words is "twenty-one million, nine hundred twenty thousand, one hundred twenty-one".