21310661 has 2 divisors, whose sum is σ = 21310662. Its totient is φ = 21310660.

The previous prime is 21310657. The next prime is 21310669. The reversal of 21310661 is 16601312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18653761 + 2656900 = 4319^2 + 1630^2 .

It is a cyclic number.

It is not a de Polignac number, because 21310661 - 2² = 21310657 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21310669) 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 as a sum of consecutive naturals, namely, 10655330 + 10655331.

It is an arithmetic number, because the mean of its divisors is an integer number (10655331).

Almost surely, 2^21310661 is an apocalyptic number.

It is an amenable number.

21310661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21310661 is an equidigital number, since it uses as much as digits as its factorization.

21310661 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 216, while the sum is 20.

The square root of 21310661 is about 4616.3471489913. The cubic root of 21310661 is about 277.2462241768.

Adding to 21310661 its reverse (16601312), we get a palindrome (37911973).

The spelling of 21310661 in words is "twenty-one million, three hundred ten thousand, six hundred sixty-one".