261551601 has 12 divisors (see below), whose sum is σ = 378060228. Its totient is φ = 174246144.

The previous prime is 261551599. The next prime is 261551617. The reversal of 261551601 is 106155162.

It is a happy number.

261551601 is a `hidden beast` number, since 2 + 6 + 1 + 5 + 51 + 601 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 111513600 + 150038001 = 10560^2 + 12249^2 .

It is not a de Polignac number, because 261551601 - 2¹ = 261551599 is a prime.

It is not an unprimeable number, because it can be changed into a prime (261551401) by changing a digit.

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 in 11 ways as a sum of consecutive naturals, for example, 4621 + ... + 23333.

It is an arithmetic number, because the mean of its divisors is an integer number (31505019).

Almost surely, 2^261551601 is an apocalyptic number.

It is an amenable number.

261551601 is a deficient number, since it is larger than the sum of its proper divisors (116508627).

261551601 is a wasteful number, since it uses less digits than its factorization.

261551601 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20272 (or 20269 counting only the distinct ones).

The product of its (nonzero) digits is 1800, while the sum is 27.

The square root of 261551601 is about 16172.5570334440. The cubic root of 261551601 is about 639.5175408529.

The spelling of 261551601 in words is "two hundred sixty-one million, five hundred fifty-one thousand, six hundred one".