261505640 has 64 divisors (see below), whose sum is σ = 659266560. Its totient is φ = 92517120.

The previous prime is 261505609. The next prime is 261505681. The reversal of 261505640 is 46505162.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 8249 + ... + 24311.

It is an arithmetic number, because the mean of its divisors is an integer number (10301040).

Almost surely, 2^261505640 is an apocalyptic number.

261505640 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 261505640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (329633280).

261505640 is an abundant number, since it is smaller than the sum of its proper divisors (397760920).

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

261505640 is a wasteful number, since it uses less digits than its factorization.

261505640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16122 (or 16118 counting only the distinct ones).

The product of its (nonzero) digits is 7200, while the sum is 29.

The square root of 261505640 is about 16171.1360145167. The cubic root of 261505640 is about 639.4800790449.

The spelling of 261505640 in words is "two hundred sixty-one million, five hundred five thousand, six hundred forty".