20856665 has 12 divisors (see below), whose sum is σ = 25342884. Its totient is φ = 16477344.

The previous prime is 20856629. The next prime is 20856679. The reversal of 20856665 is 56665802.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 6801664 + 14055001 = 2608^2 + 3749^2 .

It is not a de Polignac number, because 20856665 - 2¹² = 20852569 is a prime.

It is a Smith number, since the sum of its digits (38) coincides with the sum of the digits of its prime factors.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 127874 + ... + 128036.

It is an arithmetic number, because the mean of its divisors is an integer number (2111907).

Almost surely, 2^20856665 is an apocalyptic number.

It is an amenable number.

20856665 is a deficient number, since it is larger than the sum of its proper divisors (4486219).

20856665 is an equidigital number, since it uses as much as digits as its factorization.

20856665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 488 (or 325 counting only the distinct ones).

The product of its (nonzero) digits is 86400, while the sum is 38.

The square root of 20856665 is about 4566.9097867157. The cubic root of 20856665 is about 275.2632850405.

The spelling of 20856665 in words is "twenty million, eight hundred fifty-six thousand, six hundred sixty-five".