261981278208 has 728 divisors, whose sum is σ = 897926317848. Its totient is φ = 75676778496.

The previous prime is 261981278189. The next prime is 261981278243. The reversal of 261981278208 is 802872189162.

261981278208 is a `hidden beast` number, since 2 + 619 + 8 + 12 + 7 + 8 + 2 + 0 + 8 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 45912489984 + 216068788224 = 214272^2 + 464832^2 .

It is a Harshad number since it is a multiple of its sum of digits (54).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 55 ways as a sum of consecutive naturals, for example, 659902266 + ... + 659902662.

Almost surely, 2^261981278208 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 261981278208, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (448963158924).

261981278208 is an abundant number, since it is smaller than the sum of its proper divisors (635945039640).

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

261981278208 is an equidigital number, since it uses as much as digits as its factorization.

261981278208 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 469 (or 432 counting only the distinct ones).

The product of its (nonzero) digits is 1548288, while the sum is 54.

The spelling of 261981278208 in words is "two hundred sixty-one billion, nine hundred eighty-one million, two hundred seventy-eight thousand, two hundred eight".