261618521 has 4 divisors (see below), whose sum is σ = 263374500. Its totient is φ = 259862544.

The previous prime is 261618509. The next prime is 261618529. The reversal of 261618521 is 125816162.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 125816162 = 2 ⋅62908081.

It can be written as a sum of positive squares in 2 ways, for example, as 74995600 + 186622921 = 8660^2 + 13661^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-261618521 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (261618529) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 877766 + ... + 878063.

It is an arithmetic number, because the mean of its divisors is an integer number (65843625).

Almost surely, 2^261618521 is an apocalyptic number.

It is an amenable number.

261618521 is a deficient number, since it is larger than the sum of its proper divisors (1755979).

261618521 is a wasteful number, since it uses less digits than its factorization.

261618521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1755978.

The product of its digits is 5760, while the sum is 32.

The square root of 261618521 is about 16174.6258380217. The cubic root of 261618521 is about 639.5720780382.

The spelling of 261618521 in words is "two hundred sixty-one million, six hundred eighteen thousand, five hundred twenty-one".