261321018 has 48 divisors (see below), whose sum is σ = 615353760. Its totient is φ = 73756704.

The previous prime is 261321017. The next prime is 261321031. The reversal of 261321018 is 810123162.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (261321017) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 19048 + ... + 29756.

It is an arithmetic number, because the mean of its divisors is an integer number (12819870).

Almost surely, 2^261321018 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 261321018, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (307676880).

261321018 is an abundant number, since it is smaller than the sum of its proper divisors (354032742).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

261321018 is a wasteful number, since it uses less digits than its factorization.

261321018 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10811 (or 10804 counting only the distinct ones).

The product of its (nonzero) digits is 576, while the sum is 24.

The square root of 261321018 is about 16165.4266259818. The cubic root of 261321018 is about 639.3295534376.

The spelling of 261321018 in words is "two hundred sixty-one million, three hundred twenty-one thousand, eighteen".