21618923 has 2 divisors, whose sum is σ = 21618924. Its totient is φ = 21618922.

The previous prime is 21618899. The next prime is 21618929. The reversal of 21618923 is 32981612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21618923 - 2¹⁰ = 21617899 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a self number, because there is not a number n which added to its sum of digits gives 21618923.

It is not a weakly prime, because it can be changed into another prime (21618929) 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, 10809461 + 10809462.

It is an arithmetic number, because the mean of its divisors is an integer number (10809462).

Almost surely, 2^21618923 is an apocalyptic number.

21618923 is a deficient number, since it is larger than the sum of its proper divisors (1).

21618923 is an equidigital number, since it uses as much as digits as its factorization.

21618923 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5184, while the sum is 32.

The square root of 21618923 is about 4649.6153604357. The cubic root of 21618923 is about 278.5766329324.

The spelling of 21618923 in words is "twenty-one million, six hundred eighteen thousand, nine hundred twenty-three".