21286861 has 4 divisors (see below), whose sum is σ = 21497724. Its totient is φ = 21076000.

The previous prime is 21286823. The next prime is 21286871. The reversal of 21286861 is 16868212.

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 18224361 + 3062500 = 4269^2 + 1750^2 .

It is a cyclic number.

It is not a de Polignac number, because 21286861 - 2¹³ = 21278669 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 (21286871) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 105280 + ... + 105481.

It is an arithmetic number, because the mean of its divisors is an integer number (5374431).

Almost surely, 2^21286861 is an apocalyptic number.

It is an amenable number.

21286861 is a deficient number, since it is larger than the sum of its proper divisors (210863).

21286861 is a wasteful number, since it uses less digits than its factorization.

21286861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 210862.

The product of its digits is 9216, while the sum is 34.

The square root of 21286861 is about 4613.7686331241. The cubic root of 21286861 is about 277.1429751023.

The spelling of 21286861 in words is "twenty-one million, two hundred eighty-six thousand, eight hundred sixty-one".