21387161 has 2 divisors, whose sum is σ = 21387162. Its totient is φ = 21387160.

The previous prime is 21387151. The next prime is 21387167. The reversal of 21387161 is 16178312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18966025 + 2421136 = 4355^2 + 1556^2 .

It is a cyclic number.

It is not a de Polignac number, because 21387161 - 2⁶ = 21387097 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21387167) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10693580 + 10693581.

It is an arithmetic number, because the mean of its divisors is an integer number (10693581).

Almost surely, 2^21387161 is an apocalyptic number.

It is an amenable number.

21387161 is a deficient number, since it is larger than the sum of its proper divisors (1).

21387161 is an equidigital number, since it uses as much as digits as its factorization.

21387161 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2016, while the sum is 29.

The square root of 21387161 is about 4624.6254983512. The cubic root of 21387161 is about 277.5775764498.

The spelling of 21387161 in words is "twenty-one million, three hundred eighty-seven thousand, one hundred sixty-one".