21864281 has 2 divisors, whose sum is σ = 21864282. Its totient is φ = 21864280.

The previous prime is 21864263. The next prime is 21864287. The reversal of 21864281 is 18246812.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16128256 + 5736025 = 4016^2 + 2395^2 .

It is a cyclic number.

It is not a de Polignac number, because 21864281 - 2⁶ = 21864217 is a prime.

It is a super-2 number, since 2×21864281² = 956093567293922, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21864287) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10932140 + 10932141.

It is an arithmetic number, because the mean of its divisors is an integer number (10932141).

Almost surely, 2^21864281 is an apocalyptic number.

It is an amenable number.

21864281 is a deficient number, since it is larger than the sum of its proper divisors (1).

21864281 is an equidigital number, since it uses as much as digits as its factorization.

21864281 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6144, while the sum is 32.

The square root of 21864281 is about 4675.9256837550. The cubic root of 21864281 is about 279.6265471930.

The spelling of 21864281 in words is "twenty-one million, eight hundred sixty-four thousand, two hundred eighty-one".