21858961 has 4 divisors (see below), whose sum is σ = 21882852. Its totient is φ = 21835072.

The previous prime is 21858931. The next prime is 21858979. The reversal of 21858961 is 16985812.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 7182400 + 14676561 = 2680^2 + 3831^2 .

It is a cyclic number.

It is not a de Polignac number, because 21858961 - 2⁵ = 21858929 is a prime.

It is a super-3 number, since 3×21858961³ (a number of 23 digits) contains 333 as substring.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

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

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21858931) 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 in 3 ways as a sum of consecutive naturals, for example, 10516 + ... + 12421.

It is an arithmetic number, because the mean of its divisors is an integer number (5470713).

Almost surely, 2^21858961 is an apocalyptic number.

It is an amenable number.

21858961 is a deficient number, since it is larger than the sum of its proper divisors (23891).

21858961 is an equidigital number, since it uses as much as digits as its factorization.

21858961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23890.

The product of its digits is 34560, while the sum is 40.

The square root of 21858961 is about 4675.3567778299. The cubic root of 21858961 is about 279.6038658480.

The spelling of 21858961 in words is "twenty-one million, eight hundred fifty-eight thousand, nine hundred sixty-one".