21872165 has 16 divisors (see below), whose sum is σ = 30695808. Its totient is φ = 14648256.

The previous prime is 21872159. The next prime is 21872171. The reversal of 21872165 is 56127812.

It is an interprime number because it is at equal distance from previous prime (21872159) and next prime (21872171).

It is not a de Polignac number, because 21872165 - 2¹⁰ = 21871141 is a prime.

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 an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5762 + ... + 8771.

It is an arithmetic number, because the mean of its divisors is an integer number (1918488).

Almost surely, 2^21872165 is an apocalyptic number.

It is an amenable number.

21872165 is a deficient number, since it is larger than the sum of its proper divisors (8823643).

21872165 is a wasteful number, since it uses less digits than its factorization.

21872165 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14588.

The product of its digits is 6720, while the sum is 32.

The square root of 21872165 is about 4676.7686493989. The cubic root of 21872165 is about 279.6601531578.

Adding to 21872165 its reverse (56127812), we get a palindrome (77999977).

The spelling of 21872165 in words is "twenty-one million, eight hundred seventy-two thousand, one hundred sixty-five".