21123917 has 2 divisors, whose sum is σ = 21123918. Its totient is φ = 21123916.

The previous prime is 21123901. The next prime is 21123983. The reversal of 21123917 is 71932112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17147881 + 3976036 = 4141^2 + 1994^2 .

It is a cyclic number.

It is not a de Polignac number, because 21123917 - 2⁴ = 21123901 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21123017) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10561958 + 10561959.

It is an arithmetic number, because the mean of its divisors is an integer number (10561959).

Almost surely, 2^21123917 is an apocalyptic number.

It is an amenable number.

21123917 is a deficient number, since it is larger than the sum of its proper divisors (1).

21123917 is an equidigital number, since it uses as much as digits as its factorization.

21123917 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 756, while the sum is 26.

The square root of 21123917 is about 4596.0762613342. The cubic root of 21123917 is about 276.4340166086.

The spelling of 21123917 in words is "twenty-one million, one hundred twenty-three thousand, nine hundred seventeen".