261564021 has 24 divisors (see below), whose sum is σ = 391716000. Its totient is φ = 167987232.

The previous prime is 261564007. The next prime is 261564031. The reversal of 261564021 is 120465162.

261564021 is a `hidden beast` number, since 2 + 6 + 15 + 640 + 2 + 1 = 666.

It is not a de Polignac number, because 261564021 - 2⁷ = 261563893 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261564001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 160750 + ... + 162368.

It is an arithmetic number, because the mean of its divisors is an integer number (16321500).

Almost surely, 2^261564021 is an apocalyptic number.

It is an amenable number.

261564021 is a deficient number, since it is larger than the sum of its proper divisors (130151979).

261564021 is a wasteful number, since it uses less digits than its factorization.

261564021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2273 (or 2270 counting only the distinct ones).

The product of its (nonzero) digits is 2880, while the sum is 27.

The square root of 261564021 is about 16172.9410126915. The cubic root of 261564021 is about 639.5276633706.

The spelling of 261564021 in words is "two hundred sixty-one million, five hundred sixty-four thousand, twenty-one".