261081216 has 144 divisors (see below), whose sum is σ = 826237230. Its totient is φ = 79073280.

The previous prime is 261081209. The next prime is 261081217. The reversal of 261081216 is 612180162.

It can be written as a sum of positive squares in only one way, i.e., 259338816 + 1742400 = 16104^2 + 1320^2 .

It is a tau number, because it is divible by the number of its divisors (144).

It is a self number, because there is not a number n which added to its sum of digits gives 261081216.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261081217) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 138456 + ... + 140328.

Almost surely, 2^261081216 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 261081216, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (413118615).

261081216 is an abundant number, since it is smaller than the sum of its proper divisors (565156014).

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

261081216 is a wasteful number, since it uses less digits than its factorization.

261081216 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1915 (or 1889 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 27.

The square root of 261081216 is about 16158.0077979929. The cubic root of 261081216 is about 639.1339327070.

The spelling of 261081216 in words is "two hundred sixty-one million, eighty-one thousand, two hundred sixteen".