21306861 has 16 divisors (see below), whose sum is σ = 31641600. Its totient is φ = 14170464.

The previous prime is 21306823. The next prime is 21306869. The reversal of 21306861 is 16860312.

It is not a de Polignac number, because 21306861 - 2¹⁵ = 21274093 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21306869) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 16020 + ... + 17298.

It is an arithmetic number, because the mean of its divisors is an integer number (1977600).

Almost surely, 2^21306861 is an apocalyptic number.

It is an amenable number.

21306861 is a deficient number, since it is larger than the sum of its proper divisors (10334739).

21306861 is a wasteful number, since it uses less digits than its factorization.

21306861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1905 (or 1899 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 21306861 is about 4615.9355498100. The cubic root of 21306861 is about 277.2297441893.

The spelling of 21306861 in words is "twenty-one million, three hundred six thousand, eight hundred sixty-one".