21561697 has 2 divisors, whose sum is σ = 21561698. Its totient is φ = 21561696.

The previous prime is 21561629. The next prime is 21561733. The reversal of 21561697 is 79616512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21077281 + 484416 = 4591^2 + 696^2 .

It is a cyclic number.

It is not a de Polignac number, because 21561697 - 2¹¹ = 21559649 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21561607) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10780848 + 10780849.

It is an arithmetic number, because the mean of its divisors is an integer number (10780849).

Almost surely, 2^21561697 is an apocalyptic number.

It is an amenable number.

21561697 is a deficient number, since it is larger than the sum of its proper divisors (1).

21561697 is an equidigital number, since it uses as much as digits as its factorization.

21561697 is an evil number, because the sum of its binary digits is even.

The product of its digits is 22680, while the sum is 37.

The square root of 21561697 is about 4643.4574403132. The cubic root of 21561697 is about 278.3306152300.

The spelling of 21561697 in words is "twenty-one million, five hundred sixty-one thousand, six hundred ninety-seven".