21705161 has 2 divisors, whose sum is σ = 21705162. Its totient is φ = 21705160.

The previous prime is 21705149. The next prime is 21705191. The reversal of 21705161 is 16150712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21529600 + 175561 = 4640^2 + 419^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21705161 is a prime.

It is a super-2 number, since 2×21705161² = 942228028071842, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21705191) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10852580 + 10852581.

It is an arithmetic number, because the mean of its divisors is an integer number (10852581).

Almost surely, 2^21705161 is an apocalyptic number.

It is an amenable number.

21705161 is a deficient number, since it is larger than the sum of its proper divisors (1).

21705161 is an equidigital number, since it uses as much as digits as its factorization.

21705161 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 420, while the sum is 23.

The square root of 21705161 is about 4658.8798009822. The cubic root of 21705161 is about 278.9465560543.

Adding to 21705161 its reverse (16150712), we get a palindrome (37855873).

The spelling of 21705161 in words is "twenty-one million, seven hundred five thousand, one hundred sixty-one".