261511221 has 16 divisors (see below), whose sum is σ = 369857664. Its totient is φ = 163789824.

The previous prime is 261511213. The next prime is 261511253. The reversal of 261511221 is 122115162.

It is not a de Polignac number, because 261511221 - 2³ = 261511213 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261511291) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 25920 + ... + 34566.

It is an arithmetic number, because the mean of its divisors is an integer number (23116104).

Almost surely, 2^261511221 is an apocalyptic number.

It is an amenable number.

261511221 is a deficient number, since it is larger than the sum of its proper divisors (108346443).

261511221 is a wasteful number, since it uses less digits than its factorization.

261511221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9260.

The product of its digits is 240, while the sum is 21.

The square root of 261511221 is about 16171.3085741383. The cubic root of 261511221 is about 639.4846282303.

Adding to 261511221 its reverse (122115162), we get a palindrome (383626383).

It can be divided in two parts, 26151 and 1221, that added together give a palindrome (27372).

The spelling of 261511221 in words is "two hundred sixty-one million, five hundred eleven thousand, two hundred twenty-one".