21021261 has 4 divisors (see below), whose sum is σ = 28028352. Its totient is φ = 14014172.

The previous prime is 21021251. The next prime is 21021263. The reversal of 21021261 is 16212012.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21021261 - 2⁵ = 21021229 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21021261.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21021263) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3503541 + ... + 3503546.

It is an arithmetic number, because the mean of its divisors is an integer number (7007088).

Almost surely, 2^21021261 is an apocalyptic number.

It is an amenable number.

21021261 is a deficient number, since it is larger than the sum of its proper divisors (7007091).

21021261 is an equidigital number, since it uses as much as digits as its factorization.

21021261 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7007090.

The product of its (nonzero) digits is 48, while the sum is 15.

The square root of 21021261 is about 4584.8948733859. The cubic root of 21021261 is about 275.9854933564.

Adding to 21021261 its reverse (16212012), we get a palindrome (37233273).

Subtracting from 21021261 its reverse (16212012), we obtain a square (4809249 = 2193²).

The spelling of 21021261 in words is "twenty-one million, twenty-one thousand, two hundred sixty-one".