261681840 has 280 divisors, whose sum is σ = 1044138528. Its totient is φ = 59719680.

The previous prime is 261681811. The next prime is 261681907. The reversal of 261681840 is 48186162.

It is a tau number, because it is divible by the number of its divisors (280).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 261681795 and 261681804.

It is an unprimeable number.

It is a polite number, since it can be written in 55 ways as a sum of consecutive naturals, for example, 407920 + ... + 408560.

Almost surely, 2^261681840 is an apocalyptic number.

261681840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 261681840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (522069264).

261681840 is an abundant number, since it is smaller than the sum of its proper divisors (782456688).

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

261681840 is an equidigital number, since it uses as much as digits as its factorization.

261681840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 679 (or 658 counting only the distinct ones).

The product of its (nonzero) digits is 18432, while the sum is 36.

The square root of 261681840 is about 16176.5830755447. The cubic root of 261681840 is about 639.6236719870.

The spelling of 261681840 in words is "two hundred sixty-one million, six hundred eighty-one thousand, eight hundred forty".