205340643421 has 4 divisors (see below), whose sum is σ = 205353697500. Its totient is φ = 205327589344.

The previous prime is 205340643407. The next prime is 205340643427. The reversal of 205340643421 is 124346043502.

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 10783784025 + 194556859396 = 103845^2 + 441086^2 .

It is a cyclic number.

It is not a de Polignac number, because 205340643421 - 2²⁵ = 205307088989 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 (205340643427) 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, 6503416 + ... + 6534913.

It is an arithmetic number, because the mean of its divisors is an integer number (51338424375).

Almost surely, 2^205340643421 is an apocalyptic number.

It is an amenable number.

205340643421 is a deficient number, since it is larger than the sum of its proper divisors (13054079).

205340643421 is a wasteful number, since it uses less digits than its factorization.

205340643421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13054078.

The product of its (nonzero) digits is 69120, while the sum is 34.

Adding to 205340643421 its reverse (124346043502), we get a palindrome (329686686923).

The spelling of 205340643421 in words is "two hundred five billion, three hundred forty million, six hundred forty-three thousand, four hundred twenty-one".