21086861 has 2 divisors, whose sum is σ = 21086862. Its totient is φ = 21086860.

The previous prime is 21086839. The next prime is 21086887. The reversal of 21086861 is 16868012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13213225 + 7873636 = 3635^2 + 2806^2 .

It is a cyclic number.

It is not a de Polignac number, because 21086861 - 2¹⁰ = 21085837 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21082861) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10543430 + 10543431.

It is an arithmetic number, because the mean of its divisors is an integer number (10543431).

Almost surely, 2^21086861 is an apocalyptic number.

It is an amenable number.

21086861 is a deficient number, since it is larger than the sum of its proper divisors (1).

21086861 is an equidigital number, since it uses as much as digits as its factorization.

21086861 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4608, while the sum is 32.

The square root of 21086861 is about 4592.0432271485. The cubic root of 21086861 is about 276.2722799609.

The spelling of 21086861 in words is "twenty-one million, eighty-six thousand, eight hundred sixty-one".