221971921 has 4 divisors (see below), whose sum is σ = 223592292. Its totient is φ = 220351552.

The previous prime is 221971913. The next prime is 221971931. The reversal of 221971921 is 129179122.

It is a happy number.

221971921 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 68707521 + 153264400 = 8289^2 + 12380^2 .

It is a cyclic number.

It is not a de Polignac number, because 221971921 - 2³ = 221971913 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (221971931) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 809980 + ... + 810253.

It is an arithmetic number, because the mean of its divisors is an integer number (55898073).

Almost surely, 2^221971921 is an apocalyptic number.

It is an amenable number.

221971921 is a deficient number, since it is larger than the sum of its proper divisors (1620371).

221971921 is a wasteful number, since it uses less digits than its factorization.

221971921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1620370.

The product of its digits is 4536, while the sum is 34.

The square root of 221971921 is about 14898.7221264107. The cubic root of 221971921 is about 605.4793650883.

The spelling of 221971921 in words is "two hundred twenty-one million, nine hundred seventy-one thousand, nine hundred twenty-one".