21651521 has 8 divisors (see below), whose sum is σ = 22037184. Its totient is φ = 21268240.

The previous prime is 21651517. The next prime is 21651529. The reversal of 21651521 is 12515612.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21651521 - 2² = 21651517 is a prime.

It is a super-2 number, since 2×21651521² = 937576723226882, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21651529) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 32831 + ... + 33483.

It is an arithmetic number, because the mean of its divisors is an integer number (2754648).

Almost surely, 2^21651521 is an apocalyptic number.

It is an amenable number.

21651521 is a deficient number, since it is larger than the sum of its proper divisors (385663).

21651521 is an equidigital number, since it uses as much as digits as its factorization.

21651521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1191.

The product of its digits is 600, while the sum is 23.

The square root of 21651521 is about 4653.1194912660. The cubic root of 21651521 is about 278.7165794757.

The spelling of 21651521 in words is "twenty-one million, six hundred fifty-one thousand, five hundred twenty-one".