21666198 has 16 divisors (see below), whose sum is σ = 43379136. Its totient is φ = 7214280.

The previous prime is 21666191. The next prime is 21666209. The reversal of 21666198 is 89166612.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21666191) 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, 7953 + ... + 10323.

It is an arithmetic number, because the mean of its divisors is an integer number (2711196).

Almost surely, 2^21666198 is an apocalyptic number.

21666198 is an abundant number, since it is smaller than the sum of its proper divisors (21712938).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21666198 is a wasteful number, since it uses less digits than its factorization.

21666198 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3899.

The product of its digits is 31104, while the sum is 39.

The square root of 21666198 is about 4654.6963381084. The cubic root of 21666198 is about 278.7795434780.

The spelling of 21666198 in words is "twenty-one million, six hundred sixty-six thousand, one hundred ninety-eight".