21858217 has 2 divisors, whose sum is σ = 21858218. Its totient is φ = 21858216.

The previous prime is 21858197. The next prime is 21858259. The reversal of 21858217 is 71285812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13220496 + 8637721 = 3636^2 + 2939^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21858217 is a prime.

It is not a weakly prime, because it can be changed into another prime (21858017) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10929108 + 10929109.

It is an arithmetic number, because the mean of its divisors is an integer number (10929109).

Almost surely, 2^21858217 is an apocalyptic number.

It is an amenable number.

21858217 is a deficient number, since it is larger than the sum of its proper divisors (1).

21858217 is an equidigital number, since it uses as much as digits as its factorization.

21858217 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 8960, while the sum is 34.

The square root of 21858217 is about 4675.2772110325. The cubic root of 21858217 is about 279.6006935772.

The spelling of 21858217 in words is "twenty-one million, eight hundred fifty-eight thousand, two hundred seventeen".