866121921 has 24 divisors (see below), whose sum is σ = 1432352064. Its totient is φ = 494039520.

The previous prime is 866121911. The next prime is 866121941. The reversal of 866121921 is 129121668.

866121921 is a `hidden beast` number, since 8 + 6 + 612 + 19 + 21 = 666.

It is not a de Polignac number, because 866121921 - 2⁵ = 866121889 is a prime.

It is not an unprimeable number, because it can be changed into a prime (866121901) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 23935 + ... + 48011.

It is an arithmetic number, because the mean of its divisors is an integer number (59681336).

Almost surely, 2^866121921 is an apocalyptic number.

It is an amenable number.

866121921 is a deficient number, since it is larger than the sum of its proper divisors (566230143).

866121921 is a wasteful number, since it uses less digits than its factorization.

866121921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24661 (or 24658 counting only the distinct ones).

The product of its digits is 10368, while the sum is 36.

The square root of 866121921 is about 29429.9493883357. The cubic root of 866121921 is about 953.2197019953.

The spelling of 866121921 in words is "eight hundred sixty-six million, one hundred twenty-one thousand, nine hundred twenty-one".