21642217 has 2 divisors, whose sum is σ = 21642218. Its totient is φ = 21642216.

The previous prime is 21642199. The next prime is 21642233. The reversal of 21642217 is 71224612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19395216 + 2247001 = 4404^2 + 1499^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21642217 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21642191 and 21642200.

It is not a weakly prime, because it can be changed into another prime (21642017) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10821108 + 10821109.

It is an arithmetic number, because the mean of its divisors is an integer number (10821109).

Almost surely, 2^21642217 is an apocalyptic number.

It is an amenable number.

21642217 is a deficient number, since it is larger than the sum of its proper divisors (1).

21642217 is an equidigital number, since it uses as much as digits as its factorization.

21642217 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1344, while the sum is 25.

The square root of 21642217 is about 4652.1196244293. The cubic root of 21642217 is about 278.6766507861.

Adding to 21642217 its reverse (71224612), we get a palindrome (92866829).

The spelling of 21642217 in words is "twenty-one million, six hundred forty-two thousand, two hundred seventeen".