21156165 has 24 divisors (see below), whose sum is σ = 36848760. Its totient is φ = 11228544.

The previous prime is 21156151. The next prime is 21156181. The reversal of 21156165 is 56165112.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 6548481 + 14607684 = 2559^2 + 3822^2 .

It is not a de Polignac number, because 21156165 - 2⁸ = 21155909 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 9279 + ... + 11331.

It is an arithmetic number, because the mean of its divisors is an integer number (1535365).

Almost surely, 2^21156165 is an apocalyptic number.

It is an amenable number.

21156165 is a deficient number, since it is larger than the sum of its proper divisors (15692595).

21156165 is a wasteful number, since it uses less digits than its factorization.

21156165 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2293 (or 2290 counting only the distinct ones).

The product of its digits is 1800, while the sum is 27.

The square root of 21156165 is about 4599.5831332850. The cubic root of 21156165 is about 276.5746141395.

It can be divided in two parts, 21156 and 165, that added together give a triangular number (21321 = T₂₀₆).

The spelling of 21156165 in words is "twenty-one million, one hundred fifty-six thousand, one hundred sixty-five".