261821261 has 4 divisors (see below), whose sum is σ = 281961372. Its totient is φ = 241681152.

The previous prime is 261821237. The next prime is 261821269. The reversal of 261821261 is 162128162.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 58216900 + 203604361 = 7630^2 + 14269^2 .

It is a cyclic number.

It is not a de Polignac number, because 261821261 - 2¹⁸ = 261559117 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261821269) 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, 10070036 + ... + 10070061.

It is an arithmetic number, because the mean of its divisors is an integer number (70490343).

Almost surely, 2^261821261 is an apocalyptic number.

It is an amenable number.

261821261 is a deficient number, since it is larger than the sum of its proper divisors (20140111).

261821261 is a wasteful number, since it uses less digits than its factorization.

261821261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20140110.

The product of its digits is 2304, while the sum is 29.

The square root of 261821261 is about 16180.8918481028. The cubic root of 261821261 is about 639.7372464701.

The spelling of 261821261 in words is "two hundred sixty-one million, eight hundred twenty-one thousand, two hundred sixty-one".