261721530 has 160 divisors (see below), whose sum is σ = 830776320. Its totient is φ = 57853440.

The previous prime is 261721529. The next prime is 261721541. The reversal of 261721530 is 35127162.

It is a happy number.

261721530 is a `hidden beast` number, since 2 + 61 + 72 + 1 + 530 = 666.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a junction number, because it is equal to n+sod(n) for n = 261721494 and 261721503.

It is an unprimeable number.

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 79 ways as a sum of consecutive naturals, for example, 175026 + ... + 176514.

It is an arithmetic number, because the mean of its divisors is an integer number (5192352).

Almost surely, 2^261721530 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 261721530, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (415388160).

261721530 is an abundant number, since it is smaller than the sum of its proper divisors (569054790).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

261721530 is a wasteful number, since it uses less digits than its factorization.

261721530 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1546 (or 1537 counting only the distinct ones).

The product of its (nonzero) digits is 2520, while the sum is 27.

The square root of 261721530 is about 16177.8098023187. The cubic root of 261721530 is about 639.6560081758.

Adding to 261721530 its reverse (35127162), we get a palindrome (296848692).

The spelling of 261721530 in words is "two hundred sixty-one million, seven hundred twenty-one thousand, five hundred thirty".