261664 has 48 divisors (see below), whose sum is σ = 603288. Its totient is φ = 110592.

The previous prime is 261643. The next prime is 261673. The reversal of 261664 is 466162.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 250000 + 11664 = 500^2 + 108^2 .

It is an unprimeable number.

261664 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7054 + ... + 7090.

2²⁶¹⁶⁶⁴ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 261664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (301644).

261664 is an abundant number, since it is smaller than the sum of its proper divisors (341624).

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

261664 is a wasteful number, since it uses less digits than its factorization.

261664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 77 (or 69 counting only the distinct ones).

The product of its digits is 1728, while the sum is 25.

The square root of 261664 is about 511.5310352266. The cubic root of 261664 is about 63.9609136339.

It can be divided in two parts, 26 and 1664, that multiplied together give a square (43264 = 208²).

The spelling of 261664 in words is "two hundred sixty-one thousand, six hundred sixty-four".