261666505 has 16 divisors (see below), whose sum is σ = 325845504. Its totient is φ = 201507840.

The previous prime is 261666487. The next prime is 261666511. The reversal of 261666505 is 505666162.

It is not a de Polignac number, because 261666505 - 2⁹ = 261665993 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 25542 + ... + 34288.

It is an arithmetic number, because the mean of its divisors is an integer number (20365344).

Almost surely, 2^261666505 is an apocalyptic number.

It is an amenable number.

261666505 is a deficient number, since it is larger than the sum of its proper divisors (64178999).

261666505 is a wasteful number, since it uses less digits than its factorization.

261666505 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8976.

The product of its (nonzero) digits is 64800, while the sum is 37.

The square root of 261666505 is about 16176.1090809873. The cubic root of 261666505 is about 639.6111773986.

The spelling of 261666505 in words is "two hundred sixty-one million, six hundred sixty-six thousand, five hundred five".