21665853 has 16 divisors (see below), whose sum is σ = 35016000. Its totient is φ = 13130640.

The previous prime is 21665827. The next prime is 21665867. The reversal of 21665853 is 35856612.

It is not a de Polignac number, because 21665853 - 2⁶ = 21665789 is a prime.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

21665853 is a modest number, since divided by 65853 gives 216 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21665873) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 36178 + ... + 36771.

It is an arithmetic number, because the mean of its divisors is an integer number (2188500).

Almost surely, 2^21665853 is an apocalyptic number.

It is an amenable number.

21665853 is a deficient number, since it is larger than the sum of its proper divisors (13350147).

21665853 is a wasteful number, since it uses less digits than its factorization.

21665853 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 72969 (or 72963 counting only the distinct ones).

The product of its digits is 43200, while the sum is 36.

The square root of 21665853 is about 4654.6592786154. The cubic root of 21665853 is about 278.7780637621.

The spelling of 21665853 in words is "twenty-one million, six hundred sixty-five thousand, eight hundred fifty-three".