213665561 has 4 divisors (see below), whose sum is σ = 222955392. Its totient is φ = 204375732.

The previous prime is 213665527. The next prime is 213665567. The reversal of 213665561 is 165566312.

213665561 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 213665561 - 2⁶ = 213665497 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (213665567) 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, 4644881 + ... + 4644926.

It is an arithmetic number, because the mean of its divisors is an integer number (55738848).

Almost surely, 2^213665561 is an apocalyptic number.

It is an amenable number.

213665561 is a deficient number, since it is larger than the sum of its proper divisors (9289831).

213665561 is an equidigital number, since it uses as much as digits as its factorization.

213665561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9289830.

The product of its digits is 32400, while the sum is 35.

The square root of 213665561 is about 14617.3034790963. The cubic root of 213665561 is about 597.8306483829.

The spelling of 213665561 in words is "two hundred thirteen million, six hundred sixty-five thousand, five hundred sixty-one".