21864989 has 2 divisors, whose sum is σ = 21864990. Its totient is φ = 21864988.

The previous prime is 21864959. The next prime is 21865001. The reversal of 21864989 is 98946812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21780889 + 84100 = 4667^2 + 290^2 .

It is a cyclic number.

It is not a de Polignac number, because 21864989 - 2²⁰ = 20816413 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21864959) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10932494 + 10932495.

It is an arithmetic number, because the mean of its divisors is an integer number (10932495).

Almost surely, 2^21864989 is an apocalyptic number.

It is an amenable number.

21864989 is a deficient number, since it is larger than the sum of its proper divisors (1).

21864989 is an equidigital number, since it uses as much as digits as its factorization.

21864989 is an evil number, because the sum of its binary digits is even.

The product of its digits is 248832, while the sum is 47.

The square root of 21864989 is about 4676.0013900768. The cubic root of 21864989 is about 279.6295654104.

The spelling of 21864989 in words is "twenty-one million, eight hundred sixty-four thousand, nine hundred eighty-nine".