261806021 has 4 divisors (see below), whose sum is σ = 261933792. Its totient is φ = 261678252.

The previous prime is 261806011. The next prime is 261806053. The reversal of 261806021 is 120608162.

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 261806021 - 2²⁶ = 194697157 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 (261806011) 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, 60761 + ... + 64926.

It is an arithmetic number, because the mean of its divisors is an integer number (65483448).

Almost surely, 2^261806021 is an apocalyptic number.

It is an amenable number.

261806021 is a deficient number, since it is larger than the sum of its proper divisors (127771).

261806021 is a wasteful number, since it uses less digits than its factorization.

261806021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 127770.

The product of its (nonzero) digits is 1152, while the sum is 26.

The square root of 261806021 is about 16180.4209154150. The cubic root of 261806021 is about 639.7248336956.

The spelling of 261806021 in words is "two hundred sixty-one million, eight hundred six thousand, twenty-one".