199661821 has 4 divisors (see below), whose sum is σ = 211406652. Its totient is φ = 187916992.

The previous prime is 199661801. The next prime is 199661831. The reversal of 199661821 is 128166991.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 187306596 + 12355225 = 13686^2 + 3515^2 .

It is a cyclic number.

It is not a de Polignac number, because 199661821 - 2²¹ = 197564669 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (199661801) 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, 5872390 + ... + 5872423.

It is an arithmetic number, because the mean of its divisors is an integer number (52851663).

Almost surely, 2^199661821 is an apocalyptic number.

It is an amenable number.

199661821 is a deficient number, since it is larger than the sum of its proper divisors (11744831).

199661821 is a wasteful number, since it uses less digits than its factorization.

199661821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11744830.

The product of its digits is 46656, while the sum is 43.

The square root of 199661821 is about 14130.1741319773. The cubic root of 199661821 is about 584.4737478889.

The spelling of 199661821 in words is "one hundred ninety-nine million, six hundred sixty-one thousand, eight hundred twenty-one".