21252661 has 4 divisors (see below), whose sum is σ = 21451392. Its totient is φ = 21053932.

The previous prime is 21252653. The next prime is 21252677. The reversal of 21252661 is 16625212.

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 21252661 - 2³ = 21252653 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 (21252611) 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, 99205 + ... + 99418.

It is an arithmetic number, because the mean of its divisors is an integer number (5362848).

Almost surely, 2^21252661 is an apocalyptic number.

It is an amenable number.

21252661 is a deficient number, since it is larger than the sum of its proper divisors (198731).

21252661 is a wasteful number, since it uses less digits than its factorization.

21252661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 198730.

The product of its digits is 1440, while the sum is 25.

The square root of 21252661 is about 4610.0608455854. The cubic root of 21252661 is about 276.9944739478.

Adding to 21252661 its reverse (16625212), we get a palindrome (37877873).

The spelling of 21252661 in words is "twenty-one million, two hundred fifty-two thousand, six hundred sixty-one".