20521261 has 4 divisors (see below), whose sum is σ = 21728412. Its totient is φ = 19314112.

The previous prime is 20521253. The next prime is 20521271. The reversal of 20521261 is 16212502.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 16212502 = 2 ⋅8106251.

It can be written as a sum of positive squares in 2 ways, for example, as 16048036 + 4473225 = 4006^2 + 2115^2 .

It is a cyclic number.

It is not a de Polignac number, because 20521261 - 2³ = 20521253 is a prime.

It is a super-2 number, since 2×20521261² = 842244306060242, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20521271) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 603550 + ... + 603583.

It is an arithmetic number, because the mean of its divisors is an integer number (5432103).

Almost surely, 2^20521261 is an apocalyptic number.

It is an amenable number.

20521261 is a deficient number, since it is larger than the sum of its proper divisors (1207151).

20521261 is a wasteful number, since it uses less digits than its factorization.

20521261 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1207150.

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

The square root of 20521261 is about 4530.0398452994. The cubic root of 20521261 is about 273.7797660203.

Adding to 20521261 its reverse (16212502), we get a palindrome (36733763).

The spelling of 20521261 in words is "twenty million, five hundred twenty-one thousand, two hundred sixty-one".