261905664 has 72 divisors (see below), whose sum is σ = 699620320. Its totient is φ = 86980608.

The previous prime is 261905659. The next prime is 261905681. The reversal of 261905664 is 466509162.

It is a congruent number.

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 7 ways as a sum of consecutive naturals, for example, 304467 + ... + 305325.

Almost surely, 2^261905664 is an apocalyptic number.

261905664 is a gapful number since it is divisible by the number (24) 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 261905664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (349810160).

261905664 is an abundant number, since it is smaller than the sum of its proper divisors (437714656).

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

261905664 is an equidigital number, since it uses as much as digits as its factorization.

261905664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1275 (or 1261 counting only the distinct ones).

The product of its (nonzero) digits is 77760, while the sum is 39.

The square root of 261905664 is about 16183.4997451108. The cubic root of 261905664 is about 639.8059828560.

The spelling of 261905664 in words is "two hundred sixty-one million, nine hundred five thousand, six hundred sixty-four".