21666601 has 4 divisors (see below), whose sum is σ = 23636304. Its totient is φ = 19696900.

The previous prime is 21666587. The next prime is 21666611. The reversal of 21666601 is 10666612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21666601 - 2¹⁷ = 21535529 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21666601.

It is not an unprimeable number, because it can be changed into a prime (21666611) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 984835 + ... + 984856.

It is an arithmetic number, because the mean of its divisors is an integer number (5909076).

Almost surely, 2^21666601 is an apocalyptic number.

It is an amenable number.

21666601 is a deficient number, since it is larger than the sum of its proper divisors (1969703).

21666601 is a wasteful number, since it uses less digits than its factorization.

21666601 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1969702.

The product of its (nonzero) digits is 2592, while the sum is 28.

The square root of 21666601 is about 4654.7396275195. The cubic root of 21666601 is about 278.7812719378.

The spelling of 21666601 in words is "twenty-one million, six hundred sixty-six thousand, six hundred one".