261724021 has 4 divisors (see below), whose sum is σ = 281856652. Its totient is φ = 241591392.

The previous prime is 261723997. The next prime is 261724037. The reversal of 261724021 is 120427162.

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 117483921 + 144240100 = 10839^2 + 12010^2 .

It is a cyclic number.

It is not a de Polignac number, because 261724021 - 2⁵ = 261723989 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261724321) 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, 10066296 + ... + 10066321.

It is an arithmetic number, because the mean of its divisors is an integer number (70464163).

Almost surely, 2^261724021 is an apocalyptic number.

It is an amenable number.

261724021 is a deficient number, since it is larger than the sum of its proper divisors (20132631).

261724021 is a wasteful number, since it uses less digits than its factorization.

261724021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20132630.

The product of its (nonzero) digits is 1344, while the sum is 25.

The square root of 261724021 is about 16177.8867903073. The cubic root of 261724021 is about 639.6580375312.

The spelling of 261724021 in words is "two hundred sixty-one million, seven hundred twenty-four thousand, twenty-one".