261249664 has 64 divisors (see below), whose sum is σ = 564417000. Its totient is φ = 120446976.

The previous prime is 261249647. The next prime is 261249671. The reversal of 261249664 is 466942162.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 3968064 + 257281600 = 1992^2 + 16040^2 .

It is a tau number, because it is divible by the number of its divisors (64).

It is a super-2 number, since 2×261249664² = 136502773880225792, which contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 280752 + ... + 281680.

Almost surely, 2^261249664 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 261249664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (282208500).

261249664 is an abundant number, since it is smaller than the sum of its proper divisors (303167336).

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

261249664 is an frugal number, since it uses more digits than its factorization.

261249664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 982 (or 944 counting only the distinct ones).

The product of its digits is 124416, while the sum is 40.

The square root of 261249664 is about 16163.2194812791. The cubic root of 261249664 is about 639.2713582542.

The spelling of 261249664 in words is "two hundred sixty-one million, two hundred forty-nine thousand, six hundred sixty-four".