21666201 has 16 divisors (see below), whose sum is σ = 30307584. Its totient is φ = 13751424.

The previous prime is 21666191. The next prime is 21666209. The reversal of 21666201 is 10266612.

It is not a de Polignac number, because 21666201 - 2⁹ = 21665689 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21666209) 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, 3141 + ... + 7293.

It is an arithmetic number, because the mean of its divisors is an integer number (1894224).

Almost surely, 2^21666201 is an apocalyptic number.

It is an amenable number.

21666201 is a deficient number, since it is larger than the sum of its proper divisors (8641383).

21666201 is a wasteful number, since it uses less digits than its factorization.

21666201 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4240.

The product of its (nonzero) digits is 864, while the sum is 24.

The square root of 21666201 is about 4654.6966603636. The cubic root of 21666201 is about 278.7795563450.

The spelling of 21666201 in words is "twenty-one million, six hundred sixty-six thousand, two hundred one".