21831217 has 2 divisors, whose sum is σ = 21831218. Its totient is φ = 21831216.

The previous prime is 21831181. The next prime is 21831253. The reversal of 21831217 is 71213812.

It is a happy number.

It is a balanced prime because it is at equal distance from previous prime (21831181) and next prime (21831253).

It can be written as a sum of positive squares in only one way, i.e., 21678336 + 152881 = 4656^2 + 391^2 .

It is a cyclic number.

It is not a de Polignac number, because 21831217 - 2¹⁵ = 21798449 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21831191 and 21831200.

It is not a weakly prime, because it can be changed into another prime (21831617) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10915608 + 10915609.

It is an arithmetic number, because the mean of its divisors is an integer number (10915609).

Almost surely, 2^21831217 is an apocalyptic number.

It is an amenable number.

21831217 is a deficient number, since it is larger than the sum of its proper divisors (1).

21831217 is an equidigital number, since it uses as much as digits as its factorization.

21831217 is an evil number, because the sum of its binary digits is even.

The product of its digits is 672, while the sum is 25.

The square root of 21831217 is about 4672.3887894738. The cubic root of 21831217 is about 279.4855221032.

The spelling of 21831217 in words is "twenty-one million, eight hundred thirty-one thousand, two hundred seventeen".