261320666 has 4 divisors (see below), whose sum is σ = 391981002. Its totient is φ = 130660332.

The previous prime is 261320629. The next prime is 261320681. The reversal of 261320666 is 666023162.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 158886025 + 102434641 = 12605^2 + 10121^2 .

It is a Curzon number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 65330165 + ... + 65330168.

Almost surely, 2^261320666 is an apocalyptic number.

261320666 is a deficient number, since it is larger than the sum of its proper divisors (130660336).

261320666 is a wasteful number, since it uses less digits than its factorization.

261320666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 130660335.

The product of its (nonzero) digits is 15552, while the sum is 32.

The square root of 261320666 is about 16165.4157385450. The cubic root of 261320666 is about 639.3292663780.

The spelling of 261320666 in words is "two hundred sixty-one million, three hundred twenty thousand, six hundred sixty-six".