261665577540655 has 16 divisors (see below), whose sum is σ = 317654863162560. Its totient is φ = 206900716925952.

The previous prime is 261665577540613. The next prime is 261665577540673. The reversal of 261665577540655 is 556045775566162.

It is a cyclic number.

It is not a de Polignac number, because 261665577540655 - 2¹⁹ = 261665577016367 is a prime.

It is a congruent 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, 355984675 + ... + 356718964.

It is an arithmetic number, because the mean of its divisors is an integer number (19853428947660).

Almost surely, 2^{261665577540655} is an apocalyptic number.

261665577540655 is a deficient number, since it is larger than the sum of its proper divisors (55989285621905).

261665577540655 is an equidigital number, since it uses as much as digits as its factorization.

261665577540655 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 712704498.

The product of its (nonzero) digits is 1587600000, while the sum is 70.

The spelling of 261665577540655 in words is "two hundred sixty-one trillion, six hundred sixty-five billion, five hundred seventy-seven million, five hundred forty thousand, six hundred fifty-five".