261821021 has 8 divisors (see below), whose sum is σ = 326426304. Its totient is φ = 204016320.

The previous prime is 261821011. The next prime is 261821033. The reversal of 261821021 is 120128162.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 261821021 - 2¹⁸ = 261558877 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 (261821011) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1700060 + ... + 1700213.

It is an arithmetic number, because the mean of its divisors is an integer number (40803288).

Almost surely, 2^261821021 is an apocalyptic number.

It is an amenable number.

261821021 is a deficient number, since it is larger than the sum of its proper divisors (64605283).

261821021 is a wasteful number, since it uses less digits than its factorization.

261821021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3400291.

The product of its (nonzero) digits is 384, while the sum is 23.

The square root of 261821021 is about 16180.8844319462. The cubic root of 261821021 is about 639.7370509971.

Adding to 261821021 its reverse (120128162), we get a palindrome (381949183).

The spelling of 261821021 in words is "two hundred sixty-one million, eight hundred twenty-one thousand, twenty-one".