20721261 has 16 divisors (see below), whose sum is σ = 30443328. Its totient is φ = 12432000.

The previous prime is 20721223. The next prime is 20721263. The reversal of 20721261 is 16212702.

It is not a de Polignac number, because 20721261 - 2⁷ = 20721133 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20721263) 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, 225 + ... + 6441.

It is an arithmetic number, because the mean of its divisors is an integer number (1902708).

Almost surely, 2^20721261 is an apocalyptic number.

It is an amenable number.

20721261 is a deficient number, since it is larger than the sum of its proper divisors (9722067).

20721261 is a wasteful number, since it uses less digits than its factorization.

20721261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6332.

The product of its (nonzero) digits is 336, while the sum is 21.

The square root of 20721261 is about 4552.0611814869. The cubic root of 20721261 is about 274.6663104108. Note that the first 3 decimals are identical.

Adding to 20721261 its reverse (16212702), we get a palindrome (36933963).

It can be divided in two parts, 2072 and 1261, that added together give a palindrome (3333).

The spelling of 20721261 in words is "twenty million, seven hundred twenty-one thousand, two hundred sixty-one".