21909161 has 2 divisors, whose sum is σ = 21909162. Its totient is φ = 21909160.

The previous prime is 21909131. The next prime is 21909163. The reversal of 21909161 is 16190912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17682025 + 4227136 = 4205^2 + 2056^2 .

It is a cyclic number.

It is not a de Polignac number, because 21909161 - 2¹⁴ = 21892777 is a prime.

It is a super-2 number, since 2×21909161² = 960022671447842, which contains 22 as substring.

Together with 21909163, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21909163) 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, 10954580 + 10954581.

It is an arithmetic number, because the mean of its divisors is an integer number (10954581).

Almost surely, 2^21909161 is an apocalyptic number.

It is an amenable number.

21909161 is a deficient number, since it is larger than the sum of its proper divisors (1).

21909161 is an equidigital number, since it uses as much as digits as its factorization.

21909161 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 972, while the sum is 29.

The square root of 21909161 is about 4680.7222733249. The cubic root of 21909161 is about 279.8177427857.

The spelling of 21909161 in words is "twenty-one million, nine hundred nine thousand, one hundred sixty-one".