21717919 has 2 divisors, whose sum is σ = 21717920. Its totient is φ = 21717918.

The previous prime is 21717907. The next prime is 21717937. The reversal of 21717919 is 91971712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21717919 - 2⁷ = 21717791 is a prime.

It is a super-2 number, since 2×21717919² = 943336011381122, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21717979) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10858959 + 10858960.

It is an arithmetic number, because the mean of its divisors is an integer number (10858960).

Almost surely, 2^21717919 is an apocalyptic number.

21717919 is a deficient number, since it is larger than the sum of its proper divisors (1).

21717919 is an equidigital number, since it uses as much as digits as its factorization.

21717919 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 7938, while the sum is 37.

The square root of 21717919 is about 4660.2488131000. The cubic root of 21717919 is about 279.0011990202.

The spelling of 21717919 in words is "twenty-one million, seven hundred seventeen thousand, nine hundred nineteen".