21646861 has 4 divisors (see below), whose sum is σ = 21736924. Its totient is φ = 21556800.

The previous prime is 21646817. The next prime is 21646879. The reversal of 21646861 is 16864612.

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 7733961 + 13912900 = 2781^2 + 3730^2 .

It is a cyclic number.

It is not a de Polignac number, because 21646861 - 2⁷ = 21646733 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21649861) 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, 44670 + ... + 45151.

It is an arithmetic number, because the mean of its divisors is an integer number (5434231).

Almost surely, 2^21646861 is an apocalyptic number.

It is an amenable number.

21646861 is a deficient number, since it is larger than the sum of its proper divisors (90063).

21646861 is an equidigital number, since it uses as much as digits as its factorization.

21646861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 90062.

The product of its digits is 13824, while the sum is 34.

The square root of 21646861 is about 4652.6187249763. The cubic root of 21646861 is about 278.6965822285.

It can be divided in two parts, 2164 and 6861, that added together give a square (9025 = 95²).

The spelling of 21646861 in words is "twenty-one million, six hundred forty-six thousand, eight hundred sixty-one".