21972217 has 2 divisors, whose sum is σ = 21972218. Its totient is φ = 21972216.

The previous prime is 21972173. The next prime is 21972229. The reversal of 21972217 is 71227912.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19749136 + 2223081 = 4444^2 + 1491^2 .

It is a cyclic number.

It is not a de Polignac number, because 21972217 - 2⁷ = 21972089 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21972257) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10986108 + 10986109.

It is an arithmetic number, because the mean of its divisors is an integer number (10986109).

Almost surely, 2^21972217 is an apocalyptic number.

It is an amenable number.

21972217 is a deficient number, since it is larger than the sum of its proper divisors (1).

21972217 is an equidigital number, since it uses as much as digits as its factorization.

21972217 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3528, while the sum is 31.

The square root of 21972217 is about 4687.4531464325. The cubic root of 21972217 is about 280.0859302585.

The spelling of 21972217 in words is "twenty-one million, nine hundred seventy-two thousand, two hundred seventeen".