261630640 has 20 divisors (see below), whose sum is σ = 608291424. Its totient is φ = 104652224.

The previous prime is 261630637. The next prime is 261630641. The reversal of 261630640 is 46036162.

It is a tau number, because it is divible by the number of its divisors (20).

It is a junction number, because it is equal to n+sod(n) for n = 261630599 and 261630608.

It is not an unprimeable number, because it can be changed into a prime (261630641) 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 3 ways as a sum of consecutive naturals, for example, 1635112 + ... + 1635271.

Almost surely, 2^261630640 is an apocalyptic number.

261630640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

261630640 is an abundant number, since it is smaller than the sum of its proper divisors (346660784).

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

261630640 is a wasteful number, since it uses less digits than its factorization.

261630640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3270396 (or 3270390 counting only the distinct ones).

The product of its (nonzero) digits is 5184, while the sum is 28.

The square root of 261630640 is about 16175.0004636785. Note that the first 3 decimals coincide. The cubic root of 261630640 is about 639.5819535550.

The spelling of 261630640 in words is "two hundred sixty-one million, six hundred thirty thousand, six hundred forty".