21864013 has 2 divisors, whose sum is σ = 21864014. Its totient is φ = 21864012.

The previous prime is 21863993. The next prime is 21864019. The reversal of 21864013 is 31046812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19954089 + 1909924 = 4467^2 + 1382^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21864013 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21864019) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10932006 + 10932007.

It is an arithmetic number, because the mean of its divisors is an integer number (10932007).

Almost surely, 2^21864013 is an apocalyptic number.

It is an amenable number.

21864013 is a deficient number, since it is larger than the sum of its proper divisors (1).

21864013 is an equidigital number, since it uses as much as digits as its factorization.

21864013 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1152, while the sum is 25.

The square root of 21864013 is about 4675.8970262400. The cubic root of 21864013 is about 279.6254046870.

The spelling of 21864013 in words is "twenty-one million, eight hundred sixty-four thousand, thirteen".