261815778 has 48 divisors (see below), whose sum is σ = 652107456. Its totient is φ = 74365920.

The previous prime is 261815767. The next prime is 261815783. The reversal of 261815778 is 877518162.

It is a happy number.

It is a Curzon number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 15793 + ... + 27803.

It is an arithmetic number, because the mean of its divisors is an integer number (13585572).

Almost surely, 2^261815778 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 261815778, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (326053728).

261815778 is an abundant number, since it is smaller than the sum of its proper divisors (390291678).

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

261815778 is a wasteful number, since it uses less digits than its factorization.

261815778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12199 (or 12196 counting only the distinct ones).

The product of its digits is 188160, while the sum is 45.

The square root of 261815778 is about 16180.7224189775. The cubic root of 261815778 is about 639.7327806960.

The spelling of 261815778 in words is "two hundred sixty-one million, eight hundred fifteen thousand, seven hundred seventy-eight".