21917999 has 2 divisors, whose sum is σ = 21918000. Its totient is φ = 21917998.

The previous prime is 21917989. The next prime is 21918007. The reversal of 21917999 is 99971912.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21917999 - 2⁴ = 21917983 is a prime.

It is a super-3 number, since 3×21917999³ (a number of 23 digits) contains 333 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21917989) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10958999 + 10959000.

It is an arithmetic number, because the mean of its divisors is an integer number (10959000).

Almost surely, 2^21917999 is an apocalyptic number.

21917999 is a deficient number, since it is larger than the sum of its proper divisors (1).

21917999 is an equidigital number, since it uses as much as digits as its factorization.

21917999 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 21917999 is about 4681.6662632016. Note that the first 3 decimals coincide. The cubic root of 21917999 is about 279.8553632245.

The spelling of 21917999 in words is "twenty-one million, nine hundred seventeen thousand, nine hundred ninety-nine".