21356917 has 2 divisors, whose sum is σ = 21356918. Its totient is φ = 21356916.

The previous prime is 21356899. The next prime is 21356927. The reversal of 21356917 is 71965312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21150801 + 206116 = 4599^2 + 454^2 .

It is a cyclic number.

It is not a de Polignac number, because 21356917 - 2¹¹ = 21354869 is a prime.

It is a super-2 number, since 2×21356917² = 912235807489778, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21356927) 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, 10678458 + 10678459.

It is an arithmetic number, because the mean of its divisors is an integer number (10678459).

Almost surely, 2^21356917 is an apocalyptic number.

It is an amenable number.

21356917 is a deficient number, since it is larger than the sum of its proper divisors (1).

21356917 is an equidigital number, since it uses as much as digits as its factorization.

21356917 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 11340, while the sum is 34.

The square root of 21356917 is about 4621.3544551354. The cubic root of 21356917 is about 277.4466721105.

The spelling of 21356917 in words is "twenty-one million, three hundred fifty-six thousand, nine hundred seventeen".