21521697 has 4 divisors (see below), whose sum is σ = 28695600. Its totient is φ = 14347796.

The previous prime is 21521693. The next prime is 21521701. The reversal of 21521697 is 79612512.

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 an interprime number because it is at equal distance from previous prime (21521693) and next prime (21521701).

It is a cyclic number.

It is not a de Polignac number, because 21521697 - 2² = 21521693 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21521693) 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, 3586947 + ... + 3586952.

It is an arithmetic number, because the mean of its divisors is an integer number (7173900).

Almost surely, 2^21521697 is an apocalyptic number.

It is an amenable number.

21521697 is a deficient number, since it is larger than the sum of its proper divisors (7173903).

21521697 is an equidigital number, since it uses as much as digits as its factorization.

21521697 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7173902.

The product of its digits is 7560, while the sum is 33.

The square root of 21521697 is about 4639.1483054544. The cubic root of 21521697 is about 278.1583944584.

It can be divided in two parts, 215 and 21697, that added together give a palindrome (21912).

The spelling of 21521697 in words is "twenty-one million, five hundred twenty-one thousand, six hundred ninety-seven".