20871665 has 32 divisors (see below), whose sum is σ = 27923616. Its totient is φ = 14909440.

The previous prime is 20871659. The next prime is 20871667. The reversal of 20871665 is 56617802.

It can be written as a sum of positive squares in 16 ways, for example, as 10942864 + 9928801 = 3308^2 + 3151^2 .

It is a de Polignac number, because none of the positive numbers 2^k-20871665 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20871667) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 184649 + ... + 184761.

It is an arithmetic number, because the mean of its divisors is an integer number (872613).

Almost surely, 2^20871665 is an apocalyptic number.

It is an amenable number.

20871665 is a deficient number, since it is larger than the sum of its proper divisors (7051951).

20871665 is a wasteful number, since it uses less digits than its factorization.

20871665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 229.

The product of its (nonzero) digits is 20160, while the sum is 35.

The square root of 20871665 is about 4568.5517398843. The cubic root of 20871665 is about 275.3292585128.

The spelling of 20871665 in words is "twenty million, eight hundred seventy-one thousand, six hundred sixty-five".