21521861 has 4 divisors (see below), whose sum is σ = 21565152. Its totient is φ = 21478572.

The previous prime is 21521849. The next prime is 21521893. The reversal of 21521861 is 16812512.

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 a de Polignac number, because none of the positive numbers 2^k-21521861 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21521861.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21521821) 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, 20891 + ... + 21896.

It is an arithmetic number, because the mean of its divisors is an integer number (5391288).

Almost surely, 2^21521861 is an apocalyptic number.

It is an amenable number.

21521861 is a deficient number, since it is larger than the sum of its proper divisors (43291).

21521861 is an equidigital number, since it uses as much as digits as its factorization.

21521861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 43290.

The product of its digits is 960, while the sum is 26.

The square root of 21521861 is about 4639.1659810789. The cubic root of 21521861 is about 278.1591009990.

The spelling of 21521861 in words is "twenty-one million, five hundred twenty-one thousand, eight hundred sixty-one".