261021520 has 20 divisors (see below), whose sum is σ = 606875220. Its totient is φ = 104408576.

The previous prime is 261021511. The next prime is 261021571. The reversal of 261021520 is 25120162.

It can be written as a sum of positive squares in 2 ways, for example, as 92852496 + 168169024 = 9636^2 + 12968^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is a super-2 number, since 2×261021520² = 136264467806220800, which contains 22 as substring.

It is a congruent number.

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 3 ways as a sum of consecutive naturals, for example, 1631305 + ... + 1631464.

It is an arithmetic number, because the mean of its divisors is an integer number (30343761).

Almost surely, 2^261021520 is an apocalyptic number.

261021520 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

261021520 is an abundant number, since it is smaller than the sum of its proper divisors (345853700).

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

261021520 is a wasteful number, since it uses less digits than its factorization.

261021520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3262782 (or 3262776 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 19.

The square root of 261021520 is about 16156.1604349548. The cubic root of 261021520 is about 639.0852165154.

Adding to 261021520 its reverse (25120162), we get a palindrome (286141682).

The spelling of 261021520 in words is "two hundred sixty-one million, twenty-one thousand, five hundred twenty".