21521261 has 4 divisors (see below), whose sum is σ = 22456992. Its totient is φ = 20585532.

The previous prime is 21521257. The next prime is 21521263. The reversal of 21521261 is 16212512.

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 21521261 - 2² = 21521257 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21521263) 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, 467831 + ... + 467876.

It is an arithmetic number, because the mean of its divisors is an integer number (5614248).

Almost surely, 2^21521261 is an apocalyptic number.

It is an amenable number.

21521261 is a deficient number, since it is larger than the sum of its proper divisors (935731).

21521261 is an equidigital number, since it uses as much as digits as its factorization.

21521261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 935730.

The product of its digits is 240, while the sum is 20.

The square root of 21521261 is about 4639.1013138322. The cubic root of 21521261 is about 278.1565160768.

Adding to 21521261 its reverse (16212512), we get a palindrome (37733773).

The spelling of 21521261 in words is "twenty-one million, five hundred twenty-one thousand, two hundred sixty-one".