21072165 has 8 divisors (see below), whose sum is σ = 33715488. Its totient is φ = 11238480.

The previous prime is 21072137. The next prime is 21072169. The reversal of 21072165 is 56127012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21072165 - 2⁵ = 21072133 is a prime.

It is a super-2 number, since 2×21072165² = 888072275574450, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21072169) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 702391 + ... + 702420.

It is an arithmetic number, because the mean of its divisors is an integer number (4214436).

Almost surely, 2^21072165 is an apocalyptic number.

It is an amenable number.

21072165 is a deficient number, since it is larger than the sum of its proper divisors (12643323).

21072165 is a wasteful number, since it uses less digits than its factorization.

21072165 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1404819.

The product of its (nonzero) digits is 840, while the sum is 24.

The square root of 21072165 is about 4590.4427891000. The cubic root of 21072165 is about 276.2080845204.

Adding to 21072165 its reverse (56127012), we get a palindrome (77199177).

The spelling of 21072165 in words is "twenty-one million, seventy-two thousand, one hundred sixty-five".