21999917 has 2 divisors, whose sum is σ = 21999918. Its totient is φ = 21999916.

The previous prime is 21999911. The next prime is 21999973. The reversal of 21999917 is 71999912.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18412681 + 3587236 = 4291^2 + 1894^2 .

It is a cyclic number.

It is not a de Polignac number, because 21999917 - 2¹⁸ = 21737773 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21999911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10999958 + 10999959.

It is an arithmetic number, because the mean of its divisors is an integer number (10999959).

Almost surely, 2^21999917 is an apocalyptic number.

It is an amenable number.

21999917 is a deficient number, since it is larger than the sum of its proper divisors (1).

21999917 is an equidigital number, since it uses as much as digits as its factorization.

21999917 is an evil number, because the sum of its binary digits is even.

The product of its digits is 91854, while the sum is 47.

The square root of 21999917 is about 4690.4069119854. The cubic root of 21999917 is about 280.2035806874.

The spelling of 21999917 in words is "twenty-one million, nine hundred ninety-nine thousand, nine hundred seventeen".