261005666 has 4 divisors (see below), whose sum is σ = 391508502. Its totient is φ = 130502832.

The previous prime is 261005639. The next prime is 261005677. The reversal of 261005666 is 666500162.

261005666 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 666500162 = 2 ⋅333250081.

It can be written as a sum of positive squares in only one way, i.e., 222875041 + 38130625 = 14929^2 + 6175^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 65251415 + ... + 65251418.

Almost surely, 2^261005666 is an apocalyptic number.

261005666 is a deficient number, since it is larger than the sum of its proper divisors (130502836).

261005666 is a wasteful number, since it uses less digits than its factorization.

261005666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 130502835.

The product of its (nonzero) digits is 12960, while the sum is 32.

The square root of 261005666 is about 16155.6697787495. The cubic root of 261005666 is about 639.0722772730.

The spelling of 261005666 in words is "two hundred sixty-one million, five thousand, six hundred sixty-six".