261664660 has 12 divisors (see below), whose sum is σ = 549495828. Its totient is φ = 104665856.

The previous prime is 261664643. The next prime is 261664691. The reversal of 261664660 is 66466162.

It can be written as a sum of positive squares in 2 ways, for example, as 106213636 + 155451024 = 10306^2 + 12468^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6541597 + ... + 6541636.

It is an arithmetic number, because the mean of its divisors is an integer number (45791319).

Almost surely, 2^261664660 is an apocalyptic number.

261664660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

261664660 is an abundant number, since it is smaller than the sum of its proper divisors (287831168).

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

261664660 is a wasteful number, since it uses less digits than its factorization.

261664660 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13083242 (or 13083240 counting only the distinct ones).

The product of its (nonzero) digits is 62208, while the sum is 37.

The square root of 261664660 is about 16176.0520523396. The cubic root of 261664660 is about 639.6096741042.

It can be divided in two parts, 2616 and 64660, that added together give a palindrome (67276).

The spelling of 261664660 in words is "two hundred sixty-one million, six hundred sixty-four thousand, six hundred sixty".