261891630 has 640 divisors, whose sum is σ = 1053803520. Its totient is φ = 44789760.

The previous prime is 261891607. The next prime is 261891631. The reversal of 261891630 is 36198162.

261891630 is a `hidden beast` number, since 2 + 6 + 18 + 9 + 1 + 630 = 666.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261891631) by changing a digit.

It is a polite number, since it can be written in 319 ways as a sum of consecutive naturals, for example, 13783761 + ... + 13783779.

It is an arithmetic number, because the mean of its divisors is an integer number (1646568).

Almost surely, 2^261891630 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 261891630, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (526901760).

261891630 is an abundant number, since it is smaller than the sum of its proper divisors (791911890).

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

261891630 is a wasteful number, since it uses less digits than its factorization.

261891630 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 86 (or 77 counting only the distinct ones).

The product of its (nonzero) digits is 15552, while the sum is 36.

The square root of 261891630 is about 16183.0661495280. The cubic root of 261891630 is about 639.7945548257.

The spelling of 261891630 in words is "two hundred sixty-one million, eight hundred ninety-one thousand, six hundred thirty".