261399057985 has 32 divisors (see below), whose sum is σ = 350373314592. Its totient is φ = 185956300800.

The previous prime is 261399057971. The next prime is 261399057991. The reversal of 261399057985 is 589750993162.

It is a Cunningham number, because it is equal to 511272²+1.

It can be written as a sum of positive squares in 16 ways, for example, as 1 + 261399057984 = 1^2 + 511272^2 .

It is not a de Polignac number, because 261399057985 - 2⁹ = 261399057473 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 295164 + ... + 780973.

It is an arithmetic number, because the mean of its divisors is an integer number (10949166081).

Almost surely, 2^261399057985 is an apocalyptic number.

It is an amenable number.

261399057985 is a deficient number, since it is larger than the sum of its proper divisors (88974256607).

261399057985 is a wasteful number, since it uses less digits than its factorization.

261399057985 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1076293.

The product of its (nonzero) digits is 36741600, while the sum is 64.

The spelling of 261399057985 in words is "two hundred sixty-one billion, three hundred ninety-nine million, fifty-seven thousand, nine hundred eighty-five".